Adding upstream version 1.22.1.upstream/1.22.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

47 files changed, 6907 insertions, 0 deletions

diff --git a/src/os/exec.go b/src/os/exec.go
new file mode 100644
index 0000000..ed5a75c
--- /dev/null
+++ b/src/os/exec.go
@@ -0,0 +1,180 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"errors"
+	"internal/testlog"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"syscall"
+	"time"
+)
+
+// ErrProcessDone indicates a Process has finished.
+var ErrProcessDone = errors.New("os: process already finished")
+
+// Process stores the information about a process created by StartProcess.
+type Process struct {
+	Pid    int
+	handle uintptr      // handle is accessed atomically on Windows
+	isdone atomic.Bool  // process has been successfully waited on
+	sigMu  sync.RWMutex // avoid race between wait and signal
+}
+
+func newProcess(pid int, handle uintptr) *Process {
+	p := &Process{Pid: pid, handle: handle}
+	runtime.SetFinalizer(p, (*Process).Release)
+	return p
+}
+
+func (p *Process) setDone() {
+	p.isdone.Store(true)
+}
+
+func (p *Process) done() bool {
+	return p.isdone.Load()
+}
+
+// ProcAttr holds the attributes that will be applied to a new process
+// started by StartProcess.
+type ProcAttr struct {
+	// If Dir is non-empty, the child changes into the directory before
+	// creating the process.
+	Dir string
+	// If Env is non-nil, it gives the environment variables for the
+	// new process in the form returned by Environ.
+	// If it is nil, the result of Environ will be used.
+	Env []string
+	// Files specifies the open files inherited by the new process. The
+	// first three entries correspond to standard input, standard output, and
+	// standard error. An implementation may support additional entries,
+	// depending on the underlying operating system. A nil entry corresponds
+	// to that file being closed when the process starts.
+	// On Unix systems, StartProcess will change these File values
+	// to blocking mode, which means that SetDeadline will stop working
+	// and calling Close will not interrupt a Read or Write.
+	Files []*File
+
+	// Operating system-specific process creation attributes.
+	// Note that setting this field means that your program
+	// may not execute properly or even compile on some
+	// operating systems.
+	Sys *syscall.SysProcAttr
+}
+
+// A Signal represents an operating system signal.
+// The usual underlying implementation is operating system-dependent:
+// on Unix it is syscall.Signal.
+type Signal interface {
+	String() string
+	Signal() // to distinguish from other Stringers
+}
+
+// Getpid returns the process id of the caller.
+func Getpid() int { return syscall.Getpid() }
+
+// Getppid returns the process id of the caller's parent.
+func Getppid() int { return syscall.Getppid() }
+
+// FindProcess looks for a running process by its pid.
+//
+// The Process it returns can be used to obtain information
+// about the underlying operating system process.
+//
+// On Unix systems, FindProcess always succeeds and returns a Process
+// for the given pid, regardless of whether the process exists. To test whether
+// the process actually exists, see whether p.Signal(syscall.Signal(0)) reports
+// an error.
+func FindProcess(pid int) (*Process, error) {
+	return findProcess(pid)
+}
+
+// StartProcess starts a new process with the program, arguments and attributes
+// specified by name, argv and attr. The argv slice will become os.Args in the
+// new process, so it normally starts with the program name.
+//
+// If the calling goroutine has locked the operating system thread
+// with runtime.LockOSThread and modified any inheritable OS-level
+// thread state (for example, Linux or Plan 9 name spaces), the new
+// process will inherit the caller's thread state.
+//
+// StartProcess is a low-level interface. The os/exec package provides
+// higher-level interfaces.
+//
+// If there is an error, it will be of type *PathError.
+func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error) {
+	testlog.Open(name)
+	return startProcess(name, argv, attr)
+}
+
+// Release releases any resources associated with the Process p,
+// rendering it unusable in the future.
+// Release only needs to be called if Wait is not.
+func (p *Process) Release() error {
+	return p.release()
+}
+
+// Kill causes the Process to exit immediately. Kill does not wait until
+// the Process has actually exited. This only kills the Process itself,
+// not any other processes it may have started.
+func (p *Process) Kill() error {
+	return p.kill()
+}
+
+// Wait waits for the Process to exit, and then returns a
+// ProcessState describing its status and an error, if any.
+// Wait releases any resources associated with the Process.
+// On most operating systems, the Process must be a child
+// of the current process or an error will be returned.
+func (p *Process) Wait() (*ProcessState, error) {
+	return p.wait()
+}
+
+// Signal sends a signal to the Process.
+// Sending Interrupt on Windows is not implemented.
+func (p *Process) Signal(sig Signal) error {
+	return p.signal(sig)
+}
+
+// UserTime returns the user CPU time of the exited process and its children.
+func (p *ProcessState) UserTime() time.Duration {
+	return p.userTime()
+}
+
+// SystemTime returns the system CPU time of the exited process and its children.
+func (p *ProcessState) SystemTime() time.Duration {
+	return p.systemTime()
+}
+
+// Exited reports whether the program has exited.
+// On Unix systems this reports true if the program exited due to calling exit,
+// but false if the program terminated due to a signal.
+func (p *ProcessState) Exited() bool {
+	return p.exited()
+}
+
+// Success reports whether the program exited successfully,
+// such as with exit status 0 on Unix.
+func (p *ProcessState) Success() bool {
+	return p.success()
+}
+
+// Sys returns system-dependent exit information about
+// the process. Convert it to the appropriate underlying
+// type, such as syscall.WaitStatus on Unix, to access its contents.
+func (p *ProcessState) Sys() any {
+	return p.sys()
+}
+
+// SysUsage returns system-dependent resource usage information about
+// the exited process. Convert it to the appropriate underlying
+// type, such as *syscall.Rusage on Unix, to access its contents.
+// (On Unix, *syscall.Rusage matches struct rusage as defined in the
+// getrusage(2) manual page.)
+func (p *ProcessState) SysUsage() any {
+	return p.sysUsage()
+}
diff --git a/src/os/exec/bench_test.go b/src/os/exec/bench_test.go
new file mode 100644
index 0000000..9a94001
--- /dev/null
+++ b/src/os/exec/bench_test.go
@@ -0,0 +1,23 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"testing"
+)
+
+func BenchmarkExecHostname(b *testing.B) {
+	b.ReportAllocs()
+	path, err := LookPath("hostname")
+	if err != nil {
+		b.Fatalf("could not find hostname: %v", err)
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if err := Command(path).Run(); err != nil {
+			b.Fatalf("hostname: %v", err)
+		}
+	}
+}
diff --git a/src/os/exec/dot_test.go b/src/os/exec/dot_test.go
new file mode 100644
index 0000000..ed4bad2
--- /dev/null
+++ b/src/os/exec/dot_test.go
@@ -0,0 +1,181 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec_test
+
+import (
+	"errors"
+	"internal/testenv"
+	"os"
+	. "os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+var pathVar string = func() string {
+	if runtime.GOOS == "plan9" {
+		return "path"
+	}
+	return "PATH"
+}()
+
+func TestLookPath(t *testing.T) {
+	testenv.MustHaveExec(t)
+	// Not parallel: uses Chdir and Setenv.
+
+	tmpDir := filepath.Join(t.TempDir(), "testdir")
+	if err := os.Mkdir(tmpDir, 0777); err != nil {
+		t.Fatal(err)
+	}
+
+	executable := "execabs-test"
+	if runtime.GOOS == "windows" {
+		executable += ".exe"
+	}
+	if err := os.WriteFile(filepath.Join(tmpDir, executable), []byte{1, 2, 3}, 0777); err != nil {
+		t.Fatal(err)
+	}
+	chdir(t, tmpDir)
+	t.Setenv("PWD", tmpDir)
+	t.Logf(". is %#q", tmpDir)
+
+	origPath := os.Getenv(pathVar)
+
+	// Add "." to PATH so that exec.LookPath looks in the current directory on all systems.
+	// And try to trick it with "../testdir" too.
+	for _, errdot := range []string{"1", "0"} {
+		t.Run("GODEBUG=execerrdot="+errdot, func(t *testing.T) {
+			t.Setenv("GODEBUG", "execerrdot="+errdot+",execwait=2")
+			for _, dir := range []string{".", "../testdir"} {
+				t.Run(pathVar+"="+dir, func(t *testing.T) {
+					t.Setenv(pathVar, dir+string(filepath.ListSeparator)+origPath)
+					good := dir + "/execabs-test"
+					if found, err := LookPath(good); err != nil || !strings.HasPrefix(found, good) {
+						t.Fatalf(`LookPath(%#q) = %#q, %v, want "%s...", nil`, good, found, err, good)
+					}
+					if runtime.GOOS == "windows" {
+						good = dir + `\execabs-test`
+						if found, err := LookPath(good); err != nil || !strings.HasPrefix(found, good) {
+							t.Fatalf(`LookPath(%#q) = %#q, %v, want "%s...", nil`, good, found, err, good)
+						}
+					}
+
+					_, err := LookPath("execabs-test")
+					if errdot == "1" {
+						if err == nil {
+							t.Fatalf("LookPath didn't fail when finding a non-relative path")
+						} else if !errors.Is(err, ErrDot) {
+							t.Fatalf("LookPath returned unexpected error: want Is ErrDot, got %q", err)
+						}
+					} else {
+						if err != nil {
+							t.Fatalf("LookPath failed unexpectedly: %v", err)
+						}
+					}
+
+					cmd := Command("execabs-test")
+					if errdot == "1" {
+						if cmd.Err == nil {
+							t.Fatalf("Command didn't fail when finding a non-relative path")
+						} else if !errors.Is(cmd.Err, ErrDot) {
+							t.Fatalf("Command returned unexpected error: want Is ErrDot, got %q", cmd.Err)
+						}
+						cmd.Err = nil
+					} else {
+						if cmd.Err != nil {
+							t.Fatalf("Command failed unexpectedly: %v", err)
+						}
+					}
+
+					// Clearing cmd.Err should let the execution proceed,
+					// and it should fail because it's not a valid binary.
+					if err := cmd.Run(); err == nil {
+						t.Fatalf("Run did not fail: expected exec error")
+					} else if errors.Is(err, ErrDot) {
+						t.Fatalf("Run returned unexpected error ErrDot: want error like ENOEXEC: %q", err)
+					}
+				})
+			}
+		})
+	}
+
+	// Test the behavior when the first entry in PATH is an absolute name for the
+	// current directory.
+	//
+	// On Windows, "." may or may not be implicitly included before the explicit
+	// %PATH%, depending on the process environment;
+	// see https://go.dev/issue/4394.
+	//
+	// If the relative entry from "." resolves to the same executable as what
+	// would be resolved from an absolute entry in %PATH% alone, LookPath should
+	// return the absolute version of the path instead of ErrDot.
+	// (See https://go.dev/issue/53536.)
+	//
+	// If PATH does not implicitly include "." (such as on Unix platforms, or on
+	// Windows configured with NoDefaultCurrentDirectoryInExePath), then this
+	// lookup should succeed regardless of the behavior for ".", so it may be
+	// useful to run as a control case even on those platforms.
+	t.Run(pathVar+"=$PWD", func(t *testing.T) {
+		t.Setenv(pathVar, tmpDir+string(filepath.ListSeparator)+origPath)
+		good := filepath.Join(tmpDir, "execabs-test")
+		if found, err := LookPath(good); err != nil || !strings.HasPrefix(found, good) {
+			t.Fatalf(`LookPath(%#q) = %#q, %v, want \"%s...\", nil`, good, found, err, good)
+		}
+
+		if found, err := LookPath("execabs-test"); err != nil || !strings.HasPrefix(found, good) {
+			t.Fatalf(`LookPath(%#q) = %#q, %v, want \"%s...\", nil`, "execabs-test", found, err, good)
+		}
+
+		cmd := Command("execabs-test")
+		if cmd.Err != nil {
+			t.Fatalf("Command(%#q).Err = %v; want nil", "execabs-test", cmd.Err)
+		}
+	})
+
+	t.Run(pathVar+"=$OTHER", func(t *testing.T) {
+		// Control case: if the lookup returns ErrDot when PATH is empty, then we
+		// know that PATH implicitly includes ".". If it does not, then we don't
+		// expect to see ErrDot at all in this test (because the path will be
+		// unambiguously absolute).
+		wantErrDot := false
+		t.Setenv(pathVar, "")
+		if found, err := LookPath("execabs-test"); errors.Is(err, ErrDot) {
+			wantErrDot = true
+		} else if err == nil {
+			t.Fatalf(`with PATH='', LookPath(%#q) = %#q; want non-nil error`, "execabs-test", found)
+		}
+
+		// Set PATH to include an explicit directory that contains a completely
+		// independent executable that happens to have the same name as an
+		// executable in ".". If "." is included implicitly, looking up the
+		// (unqualified) executable name will return ErrDot; otherwise, the
+		// executable in "." should have no effect and the lookup should
+		// unambiguously resolve to the directory in PATH.
+
+		dir := t.TempDir()
+		executable := "execabs-test"
+		if runtime.GOOS == "windows" {
+			executable += ".exe"
+		}
+		if err := os.WriteFile(filepath.Join(dir, executable), []byte{1, 2, 3}, 0777); err != nil {
+			t.Fatal(err)
+		}
+		t.Setenv(pathVar, dir+string(filepath.ListSeparator)+origPath)
+
+		found, err := LookPath("execabs-test")
+		if wantErrDot {
+			wantFound := filepath.Join(".", executable)
+			if found != wantFound || !errors.Is(err, ErrDot) {
+				t.Fatalf(`LookPath(%#q) = %#q, %v, want %#q, Is ErrDot`, "execabs-test", found, err, wantFound)
+			}
+		} else {
+			wantFound := filepath.Join(dir, executable)
+			if found != wantFound || err != nil {
+				t.Fatalf(`LookPath(%#q) = %#q, %v, want %#q, nil`, "execabs-test", found, err, wantFound)
+			}
+		}
+	})
+}
diff --git a/src/os/exec/env_test.go b/src/os/exec/env_test.go
new file mode 100644
index 0000000..ea06af3
--- /dev/null
+++ b/src/os/exec/env_test.go
@@ -0,0 +1,67 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestDedupEnv(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		noCase  bool
+		nulOK   bool
+		in      []string
+		want    []string
+		wantErr bool
+	}{
+		{
+			noCase: true,
+			in:     []string{"k1=v1", "k2=v2", "K1=v3"},
+			want:   []string{"k2=v2", "K1=v3"},
+		},
+		{
+			noCase: false,
+			in:     []string{"k1=v1", "K1=V2", "k1=v3"},
+			want:   []string{"K1=V2", "k1=v3"},
+		},
+		{
+			in:   []string{"=a", "=b", "foo", "bar"},
+			want: []string{"=b", "foo", "bar"},
+		},
+		{
+			// #49886: preserve weird Windows keys with leading "=" signs.
+			noCase: true,
+			in:     []string{`=C:=C:\golang`, `=D:=D:\tmp`, `=D:=D:\`},
+			want:   []string{`=C:=C:\golang`, `=D:=D:\`},
+		},
+		{
+			// #52436: preserve invalid key-value entries (for now).
+			// (Maybe filter them out or error out on them at some point.)
+			in:   []string{"dodgy", "entries"},
+			want: []string{"dodgy", "entries"},
+		},
+		{
+			// Filter out entries containing NULs.
+			in:      []string{"A=a\x00b", "B=b", "C\x00C=c"},
+			want:    []string{"B=b"},
+			wantErr: true,
+		},
+		{
+			// Plan 9 needs to preserve environment variables with NUL (#56544).
+			nulOK: true,
+			in:    []string{"path=one\x00two"},
+			want:  []string{"path=one\x00two"},
+		},
+	}
+	for _, tt := range tests {
+		got, err := dedupEnvCase(tt.noCase, tt.nulOK, tt.in)
+		if !reflect.DeepEqual(got, tt.want) || (err != nil) != tt.wantErr {
+			t.Errorf("Dedup(%v, %q) = %q, %v; want %q, error:%v", tt.noCase, tt.in, got, err, tt.want, tt.wantErr)
+		}
+	}
+}
diff --git a/src/os/exec/example_test.go b/src/os/exec/example_test.go
new file mode 100644
index 0000000..150f5cf
--- /dev/null
+++ b/src/os/exec/example_test.go
@@ -0,0 +1,169 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec_test
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+	"time"
+)
+
+func ExampleLookPath() {
+	path, err := exec.LookPath("fortune")
+	if err != nil {
+		log.Fatal("installing fortune is in your future")
+	}
+	fmt.Printf("fortune is available at %s\n", path)
+}
+
+func ExampleCommand() {
+	cmd := exec.Command("tr", "a-z", "A-Z")
+	cmd.Stdin = strings.NewReader("some input")
+	var out strings.Builder
+	cmd.Stdout = &out
+	err := cmd.Run()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("in all caps: %q\n", out.String())
+}
+
+func ExampleCommand_environment() {
+	cmd := exec.Command("prog")
+	cmd.Env = append(os.Environ(),
+		"FOO=duplicate_value", // ignored
+		"FOO=actual_value",    // this value is used
+	)
+	if err := cmd.Run(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func ExampleCmd_Output() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+
+func ExampleCmd_Run() {
+	cmd := exec.Command("sleep", "1")
+	log.Printf("Running command and waiting for it to finish...")
+	err := cmd.Run()
+	log.Printf("Command finished with error: %v", err)
+}
+
+func ExampleCmd_Start() {
+	cmd := exec.Command("sleep", "5")
+	err := cmd.Start()
+	if err != nil {
+		log.Fatal(err)
+	}
+	log.Printf("Waiting for command to finish...")
+	err = cmd.Wait()
+	log.Printf("Command finished with error: %v", err)
+}
+
+func ExampleCmd_StdoutPipe() {
+	cmd := exec.Command("echo", "-n", `{"Name": "Bob", "Age": 32}`)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := cmd.Start(); err != nil {
+		log.Fatal(err)
+	}
+	var person struct {
+		Name string
+		Age  int
+	}
+	if err := json.NewDecoder(stdout).Decode(&person); err != nil {
+		log.Fatal(err)
+	}
+	if err := cmd.Wait(); err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s is %d years old\n", person.Name, person.Age)
+}
+
+func ExampleCmd_StdinPipe() {
+	cmd := exec.Command("cat")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	go func() {
+		defer stdin.Close()
+		io.WriteString(stdin, "values written to stdin are passed to cmd's standard input")
+	}()
+
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("%s\n", out)
+}
+
+func ExampleCmd_StderrPipe() {
+	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		log.Fatal(err)
+	}
+
+	slurp, _ := io.ReadAll(stderr)
+	fmt.Printf("%s\n", slurp)
+
+	if err := cmd.Wait(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func ExampleCmd_CombinedOutput() {
+	cmd := exec.Command("sh", "-c", "echo stdout; echo 1>&2 stderr")
+	stdoutStderr, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s\n", stdoutStderr)
+}
+
+func ExampleCmd_Environ() {
+	cmd := exec.Command("pwd")
+
+	// Set Dir before calling cmd.Environ so that it will include an
+	// updated PWD variable (on platforms where that is used).
+	cmd.Dir = ".."
+	cmd.Env = append(cmd.Environ(), "POSIXLY_CORRECT=1")
+
+	out, err := cmd.Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s\n", out)
+}
+
+func ExampleCommandContext() {
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+
+	if err := exec.CommandContext(ctx, "sleep", "5").Run(); err != nil {
+		// This will fail after 100 milliseconds. The 5 second sleep
+		// will be interrupted.
+	}
+}
diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
new file mode 100644
index 0000000..c88ee7f
--- /dev/null
+++ b/src/os/exec/exec.go
@@ -0,0 +1,1303 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package exec runs external commands. It wraps os.StartProcess to make it
+// easier to remap stdin and stdout, connect I/O with pipes, and do other
+// adjustments.
+//
+// Unlike the "system" library call from C and other languages, the
+// os/exec package intentionally does not invoke the system shell and
+// does not expand any glob patterns or handle other expansions,
+// pipelines, or redirections typically done by shells. The package
+// behaves more like C's "exec" family of functions. To expand glob
+// patterns, either call the shell directly, taking care to escape any
+// dangerous input, or use the path/filepath package's Glob function.
+// To expand environment variables, use package os's ExpandEnv.
+//
+// Note that the examples in this package assume a Unix system.
+// They may not run on Windows, and they do not run in the Go Playground
+// used by golang.org and godoc.org.
+//
+// # Executables in the current directory
+//
+// The functions Command and LookPath look for a program
+// in the directories listed in the current path, following the
+// conventions of the host operating system.
+// Operating systems have for decades included the current
+// directory in this search, sometimes implicitly and sometimes
+// configured explicitly that way by default.
+// Modern practice is that including the current directory
+// is usually unexpected and often leads to security problems.
+//
+// To avoid those security problems, as of Go 1.19, this package will not resolve a program
+// using an implicit or explicit path entry relative to the current directory.
+// That is, if you run exec.LookPath("go"), it will not successfully return
+// ./go on Unix nor .\go.exe on Windows, no matter how the path is configured.
+// Instead, if the usual path algorithms would result in that answer,
+// these functions return an error err satisfying errors.Is(err, ErrDot).
+//
+// For example, consider these two program snippets:
+//
+//	path, err := exec.LookPath("prog")
+//	if err != nil {
+//		log.Fatal(err)
+//	}
+//	use(path)
+//
+// and
+//
+//	cmd := exec.Command("prog")
+//	if err := cmd.Run(); err != nil {
+//		log.Fatal(err)
+//	}
+//
+// These will not find and run ./prog or .\prog.exe,
+// no matter how the current path is configured.
+//
+// Code that always wants to run a program from the current directory
+// can be rewritten to say "./prog" instead of "prog".
+//
+// Code that insists on including results from relative path entries
+// can instead override the error using an errors.Is check:
+//
+//	path, err := exec.LookPath("prog")
+//	if errors.Is(err, exec.ErrDot) {
+//		err = nil
+//	}
+//	if err != nil {
+//		log.Fatal(err)
+//	}
+//	use(path)
+//
+// and
+//
+//	cmd := exec.Command("prog")
+//	if errors.Is(cmd.Err, exec.ErrDot) {
+//		cmd.Err = nil
+//	}
+//	if err := cmd.Run(); err != nil {
+//		log.Fatal(err)
+//	}
+//
+// Setting the environment variable GODEBUG=execerrdot=0
+// disables generation of ErrDot entirely, temporarily restoring the pre-Go 1.19
+// behavior for programs that are unable to apply more targeted fixes.
+// A future version of Go may remove support for this variable.
+//
+// Before adding such overrides, make sure you understand the
+// security implications of doing so.
+// See https://go.dev/blog/path-security for more information.
+package exec
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"internal/godebug"
+	"internal/syscall/execenv"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+)
+
+// Error is returned by LookPath when it fails to classify a file as an
+// executable.
+type Error struct {
+	// Name is the file name for which the error occurred.
+	Name string
+	// Err is the underlying error.
+	Err error
+}
+
+func (e *Error) Error() string {
+	return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
+}
+
+func (e *Error) Unwrap() error { return e.Err }
+
+// ErrWaitDelay is returned by (*Cmd).Wait if the process exits with a
+// successful status code but its output pipes are not closed before the
+// command's WaitDelay expires.
+var ErrWaitDelay = errors.New("exec: WaitDelay expired before I/O complete")
+
+// wrappedError wraps an error without relying on fmt.Errorf.
+type wrappedError struct {
+	prefix string
+	err    error
+}
+
+func (w wrappedError) Error() string {
+	return w.prefix + ": " + w.err.Error()
+}
+
+func (w wrappedError) Unwrap() error {
+	return w.err
+}
+
+// Cmd represents an external command being prepared or run.
+//
+// A Cmd cannot be reused after calling its Run, Output or CombinedOutput
+// methods.
+type Cmd struct {
+	// Path is the path of the command to run.
+	//
+	// This is the only field that must be set to a non-zero
+	// value. If Path is relative, it is evaluated relative
+	// to Dir.
+	Path string
+
+	// Args holds command line arguments, including the command as Args[0].
+	// If the Args field is empty or nil, Run uses {Path}.
+	//
+	// In typical use, both Path and Args are set by calling Command.
+	Args []string
+
+	// Env specifies the environment of the process.
+	// Each entry is of the form "key=value".
+	// If Env is nil, the new process uses the current process's
+	// environment.
+	// If Env contains duplicate environment keys, only the last
+	// value in the slice for each duplicate key is used.
+	// As a special case on Windows, SYSTEMROOT is always added if
+	// missing and not explicitly set to the empty string.
+	Env []string
+
+	// Dir specifies the working directory of the command.
+	// If Dir is the empty string, Run runs the command in the
+	// calling process's current directory.
+	Dir string
+
+	// Stdin specifies the process's standard input.
+	//
+	// If Stdin is nil, the process reads from the null device (os.DevNull).
+	//
+	// If Stdin is an *os.File, the process's standard input is connected
+	// directly to that file.
+	//
+	// Otherwise, during the execution of the command a separate
+	// goroutine reads from Stdin and delivers that data to the command
+	// over a pipe. In this case, Wait does not complete until the goroutine
+	// stops copying, either because it has reached the end of Stdin
+	// (EOF or a read error), or because writing to the pipe returned an error,
+	// or because a nonzero WaitDelay was set and expired.
+	Stdin io.Reader
+
+	// Stdout and Stderr specify the process's standard output and error.
+	//
+	// If either is nil, Run connects the corresponding file descriptor
+	// to the null device (os.DevNull).
+	//
+	// If either is an *os.File, the corresponding output from the process
+	// is connected directly to that file.
+	//
+	// Otherwise, during the execution of the command a separate goroutine
+	// reads from the process over a pipe and delivers that data to the
+	// corresponding Writer. In this case, Wait does not complete until the
+	// goroutine reaches EOF or encounters an error or a nonzero WaitDelay
+	// expires.
+	//
+	// If Stdout and Stderr are the same writer, and have a type that can
+	// be compared with ==, at most one goroutine at a time will call Write.
+	Stdout io.Writer
+	Stderr io.Writer
+
+	// ExtraFiles specifies additional open files to be inherited by the
+	// new process. It does not include standard input, standard output, or
+	// standard error. If non-nil, entry i becomes file descriptor 3+i.
+	//
+	// ExtraFiles is not supported on Windows.
+	ExtraFiles []*os.File
+
+	// SysProcAttr holds optional, operating system-specific attributes.
+	// Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
+	SysProcAttr *syscall.SysProcAttr
+
+	// Process is the underlying process, once started.
+	Process *os.Process
+
+	// ProcessState contains information about an exited process.
+	// If the process was started successfully, Wait or Run will
+	// populate its ProcessState when the command completes.
+	ProcessState *os.ProcessState
+
+	// ctx is the context passed to CommandContext, if any.
+	ctx context.Context
+
+	Err error // LookPath error, if any.
+
+	// If Cancel is non-nil, the command must have been created with
+	// CommandContext and Cancel will be called when the command's
+	// Context is done. By default, CommandContext sets Cancel to
+	// call the Kill method on the command's Process.
+	//
+	// Typically a custom Cancel will send a signal to the command's
+	// Process, but it may instead take other actions to initiate cancellation,
+	// such as closing a stdin or stdout pipe or sending a shutdown request on a
+	// network socket.
+	//
+	// If the command exits with a success status after Cancel is
+	// called, and Cancel does not return an error equivalent to
+	// os.ErrProcessDone, then Wait and similar methods will return a non-nil
+	// error: either an error wrapping the one returned by Cancel,
+	// or the error from the Context.
+	// (If the command exits with a non-success status, or Cancel
+	// returns an error that wraps os.ErrProcessDone, Wait and similar methods
+	// continue to return the command's usual exit status.)
+	//
+	// If Cancel is set to nil, nothing will happen immediately when the command's
+	// Context is done, but a nonzero WaitDelay will still take effect. That may
+	// be useful, for example, to work around deadlocks in commands that do not
+	// support shutdown signals but are expected to always finish quickly.
+	//
+	// Cancel will not be called if Start returns a non-nil error.
+	Cancel func() error
+
+	// If WaitDelay is non-zero, it bounds the time spent waiting on two sources
+	// of unexpected delay in Wait: a child process that fails to exit after the
+	// associated Context is canceled, and a child process that exits but leaves
+	// its I/O pipes unclosed.
+	//
+	// The WaitDelay timer starts when either the associated Context is done or a
+	// call to Wait observes that the child process has exited, whichever occurs
+	// first. When the delay has elapsed, the command shuts down the child process
+	// and/or its I/O pipes.
+	//
+	// If the child process has failed to exit — perhaps because it ignored or
+	// failed to receive a shutdown signal from a Cancel function, or because no
+	// Cancel function was set — then it will be terminated using os.Process.Kill.
+	//
+	// Then, if the I/O pipes communicating with the child process are still open,
+	// those pipes are closed in order to unblock any goroutines currently blocked
+	// on Read or Write calls.
+	//
+	// If pipes are closed due to WaitDelay, no Cancel call has occurred,
+	// and the command has otherwise exited with a successful status, Wait and
+	// similar methods will return ErrWaitDelay instead of nil.
+	//
+	// If WaitDelay is zero (the default), I/O pipes will be read until EOF,
+	// which might not occur until orphaned subprocesses of the command have
+	// also closed their descriptors for the pipes.
+	WaitDelay time.Duration
+
+	// childIOFiles holds closers for any of the child process's
+	// stdin, stdout, and/or stderr files that were opened by the Cmd itself
+	// (not supplied by the caller). These should be closed as soon as they
+	// are inherited by the child process.
+	childIOFiles []io.Closer
+
+	// parentIOPipes holds closers for the parent's end of any pipes
+	// connected to the child's stdin, stdout, and/or stderr streams
+	// that were opened by the Cmd itself (not supplied by the caller).
+	// These should be closed after Wait sees the command and copying
+	// goroutines exit, or after WaitDelay has expired.
+	parentIOPipes []io.Closer
+
+	// goroutine holds a set of closures to execute to copy data
+	// to and/or from the command's I/O pipes.
+	goroutine []func() error
+
+	// If goroutineErr is non-nil, it receives the first error from a copying
+	// goroutine once all such goroutines have completed.
+	// goroutineErr is set to nil once its error has been received.
+	goroutineErr <-chan error
+
+	// If ctxResult is non-nil, it receives the result of watchCtx exactly once.
+	ctxResult <-chan ctxResult
+
+	// The stack saved when the Command was created, if GODEBUG contains
+	// execwait=2. Used for debugging leaks.
+	createdByStack []byte
+
+	// For a security release long ago, we created x/sys/execabs,
+	// which manipulated the unexported lookPathErr error field
+	// in this struct. For Go 1.19 we exported the field as Err error,
+	// above, but we have to keep lookPathErr around for use by
+	// old programs building against new toolchains.
+	// The String and Start methods look for an error in lookPathErr
+	// in preference to Err, to preserve the errors that execabs sets.
+	//
+	// In general we don't guarantee misuse of reflect like this,
+	// but the misuse of reflect was by us, the best of various bad
+	// options to fix the security problem, and people depend on
+	// those old copies of execabs continuing to work.
+	// The result is that we have to leave this variable around for the
+	// rest of time, a compatibility scar.
+	//
+	// See https://go.dev/blog/path-security
+	// and https://go.dev/issue/43724 for more context.
+	lookPathErr error
+}
+
+// A ctxResult reports the result of watching the Context associated with a
+// running command (and sending corresponding signals if needed).
+type ctxResult struct {
+	err error
+
+	// If timer is non-nil, it expires after WaitDelay has elapsed after
+	// the Context is done.
+	//
+	// (If timer is nil, that means that the Context was not done before the
+	// command completed, or no WaitDelay was set, or the WaitDelay already
+	// expired and its effect was already applied.)
+	timer *time.Timer
+}
+
+var execwait = godebug.New("#execwait")
+var execerrdot = godebug.New("execerrdot")
+
+// Command returns the Cmd struct to execute the named program with
+// the given arguments.
+//
+// It sets only the Path and Args in the returned structure.
+//
+// If name contains no path separators, Command uses LookPath to
+// resolve name to a complete path if possible. Otherwise it uses name
+// directly as Path.
+//
+// The returned Cmd's Args field is constructed from the command name
+// followed by the elements of arg, so arg should not include the
+// command name itself. For example, Command("echo", "hello").
+// Args[0] is always name, not the possibly resolved Path.
+//
+// On Windows, processes receive the whole command line as a single string
+// and do their own parsing. Command combines and quotes Args into a command
+// line string with an algorithm compatible with applications using
+// CommandLineToArgvW (which is the most common way). Notable exceptions are
+// msiexec.exe and cmd.exe (and thus, all batch files), which have a different
+// unquoting algorithm. In these or other similar cases, you can do the
+// quoting yourself and provide the full command line in SysProcAttr.CmdLine,
+// leaving Args empty.
+func Command(name string, arg ...string) *Cmd {
+	cmd := &Cmd{
+		Path: name,
+		Args: append([]string{name}, arg...),
+	}
+
+	if v := execwait.Value(); v != "" {
+		if v == "2" {
+			// Obtain the caller stack. (This is equivalent to runtime/debug.Stack,
+			// copied to avoid importing the whole package.)
+			stack := make([]byte, 1024)
+			for {
+				n := runtime.Stack(stack, false)
+				if n < len(stack) {
+					stack = stack[:n]
+					break
+				}
+				stack = make([]byte, 2*len(stack))
+			}
+
+			if i := bytes.Index(stack, []byte("\nos/exec.Command(")); i >= 0 {
+				stack = stack[i+1:]
+			}
+			cmd.createdByStack = stack
+		}
+
+		runtime.SetFinalizer(cmd, func(c *Cmd) {
+			if c.Process != nil && c.ProcessState == nil {
+				debugHint := ""
+				if c.createdByStack == nil {
+					debugHint = " (set GODEBUG=execwait=2 to capture stacks for debugging)"
+				} else {
+					os.Stderr.WriteString("GODEBUG=execwait=2 detected a leaked exec.Cmd created by:\n")
+					os.Stderr.Write(c.createdByStack)
+					os.Stderr.WriteString("\n")
+					debugHint = ""
+				}
+				panic("exec: Cmd started a Process but leaked without a call to Wait" + debugHint)
+			}
+		})
+	}
+
+	if filepath.Base(name) == name {
+		lp, err := LookPath(name)
+		if lp != "" {
+			// Update cmd.Path even if err is non-nil.
+			// If err is ErrDot (especially on Windows), lp may include a resolved
+			// extension (like .exe or .bat) that should be preserved.
+			cmd.Path = lp
+		}
+		if err != nil {
+			cmd.Err = err
+		}
+	} else if runtime.GOOS == "windows" && filepath.IsAbs(name) {
+		// We may need to add a filename extension from PATHEXT
+		// or verify an extension that is already present.
+		// Since the path is absolute, its extension should be unambiguous
+		// and independent of cmd.Dir, and we can go ahead and update cmd.Path to
+		// reflect it.
+		//
+		// Note that we cannot add an extension here for relative paths, because
+		// cmd.Dir may be set after we return from this function and that may cause
+		// the command to resolve to a different extension.
+		lp, err := lookExtensions(name, "")
+		if lp != "" {
+			cmd.Path = lp
+		}
+		if err != nil {
+			cmd.Err = err
+		}
+	}
+	return cmd
+}
+
+// CommandContext is like Command but includes a context.
+//
+// The provided context is used to interrupt the process
+// (by calling cmd.Cancel or os.Process.Kill)
+// if the context becomes done before the command completes on its own.
+//
+// CommandContext sets the command's Cancel function to invoke the Kill method
+// on its Process, and leaves its WaitDelay unset. The caller may change the
+// cancellation behavior by modifying those fields before starting the command.
+func CommandContext(ctx context.Context, name string, arg ...string) *Cmd {
+	if ctx == nil {
+		panic("nil Context")
+	}
+	cmd := Command(name, arg...)
+	cmd.ctx = ctx
+	cmd.Cancel = func() error {
+		return cmd.Process.Kill()
+	}
+	return cmd
+}
+
+// String returns a human-readable description of c.
+// It is intended only for debugging.
+// In particular, it is not suitable for use as input to a shell.
+// The output of String may vary across Go releases.
+func (c *Cmd) String() string {
+	if c.Err != nil || c.lookPathErr != nil {
+		// failed to resolve path; report the original requested path (plus args)
+		return strings.Join(c.Args, " ")
+	}
+	// report the exact executable path (plus args)
+	b := new(strings.Builder)
+	b.WriteString(c.Path)
+	for _, a := range c.Args[1:] {
+		b.WriteByte(' ')
+		b.WriteString(a)
+	}
+	return b.String()
+}
+
+// interfaceEqual protects against panics from doing equality tests on
+// two interfaces with non-comparable underlying types.
+func interfaceEqual(a, b any) bool {
+	defer func() {
+		recover()
+	}()
+	return a == b
+}
+
+func (c *Cmd) argv() []string {
+	if len(c.Args) > 0 {
+		return c.Args
+	}
+	return []string{c.Path}
+}
+
+func (c *Cmd) childStdin() (*os.File, error) {
+	if c.Stdin == nil {
+		f, err := os.Open(os.DevNull)
+		if err != nil {
+			return nil, err
+		}
+		c.childIOFiles = append(c.childIOFiles, f)
+		return f, nil
+	}
+
+	if f, ok := c.Stdin.(*os.File); ok {
+		return f, nil
+	}
+
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	c.childIOFiles = append(c.childIOFiles, pr)
+	c.parentIOPipes = append(c.parentIOPipes, pw)
+	c.goroutine = append(c.goroutine, func() error {
+		_, err := io.Copy(pw, c.Stdin)
+		if skipStdinCopyError(err) {
+			err = nil
+		}
+		if err1 := pw.Close(); err == nil {
+			err = err1
+		}
+		return err
+	})
+	return pr, nil
+}
+
+func (c *Cmd) childStdout() (*os.File, error) {
+	return c.writerDescriptor(c.Stdout)
+}
+
+func (c *Cmd) childStderr(childStdout *os.File) (*os.File, error) {
+	if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
+		return childStdout, nil
+	}
+	return c.writerDescriptor(c.Stderr)
+}
+
+// writerDescriptor returns an os.File to which the child process
+// can write to send data to w.
+//
+// If w is nil, writerDescriptor returns a File that writes to os.DevNull.
+func (c *Cmd) writerDescriptor(w io.Writer) (*os.File, error) {
+	if w == nil {
+		f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
+		if err != nil {
+			return nil, err
+		}
+		c.childIOFiles = append(c.childIOFiles, f)
+		return f, nil
+	}
+
+	if f, ok := w.(*os.File); ok {
+		return f, nil
+	}
+
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	c.childIOFiles = append(c.childIOFiles, pw)
+	c.parentIOPipes = append(c.parentIOPipes, pr)
+	c.goroutine = append(c.goroutine, func() error {
+		_, err := io.Copy(w, pr)
+		pr.Close() // in case io.Copy stopped due to write error
+		return err
+	})
+	return pw, nil
+}
+
+func closeDescriptors(closers []io.Closer) {
+	for _, fd := range closers {
+		fd.Close()
+	}
+}
+
+// Run starts the specified command and waits for it to complete.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command starts but does not complete successfully, the error is of
+// type *ExitError. Other error types may be returned for other situations.
+//
+// If the calling goroutine has locked the operating system thread
+// with runtime.LockOSThread and modified any inheritable OS-level
+// thread state (for example, Linux or Plan 9 name spaces), the new
+// process will inherit the caller's thread state.
+func (c *Cmd) Run() error {
+	if err := c.Start(); err != nil {
+		return err
+	}
+	return c.Wait()
+}
+
+// Start starts the specified command but does not wait for it to complete.
+//
+// If Start returns successfully, the c.Process field will be set.
+//
+// After a successful call to Start the Wait method must be called in
+// order to release associated system resources.
+func (c *Cmd) Start() error {
+	// Check for doubled Start calls before we defer failure cleanup. If the prior
+	// call to Start succeeded, we don't want to spuriously close its pipes.
+	if c.Process != nil {
+		return errors.New("exec: already started")
+	}
+
+	started := false
+	defer func() {
+		closeDescriptors(c.childIOFiles)
+		c.childIOFiles = nil
+
+		if !started {
+			closeDescriptors(c.parentIOPipes)
+			c.parentIOPipes = nil
+		}
+	}()
+
+	if c.Path == "" && c.Err == nil && c.lookPathErr == nil {
+		c.Err = errors.New("exec: no command")
+	}
+	if c.Err != nil || c.lookPathErr != nil {
+		if c.lookPathErr != nil {
+			return c.lookPathErr
+		}
+		return c.Err
+	}
+	lp := c.Path
+	if runtime.GOOS == "windows" && !filepath.IsAbs(c.Path) {
+		// If c.Path is relative, we had to wait until now
+		// to resolve it in case c.Dir was changed.
+		// (If it is absolute, we already resolved its extension in Command
+		// and shouldn't need to do so again.)
+		//
+		// Unfortunately, we cannot write the result back to c.Path because programs
+		// may assume that they can call Start concurrently with reading the path.
+		// (It is safe and non-racy to do so on Unix platforms, and users might not
+		// test with the race detector on all platforms;
+		// see https://go.dev/issue/62596.)
+		//
+		// So we will pass the fully resolved path to os.StartProcess, but leave
+		// c.Path as is: missing a bit of logging information seems less harmful
+		// than triggering a surprising data race, and if the user really cares
+		// about that bit of logging they can always use LookPath to resolve it.
+		var err error
+		lp, err = lookExtensions(c.Path, c.Dir)
+		if err != nil {
+			return err
+		}
+	}
+	if c.Cancel != nil && c.ctx == nil {
+		return errors.New("exec: command with a non-nil Cancel was not created with CommandContext")
+	}
+	if c.ctx != nil {
+		select {
+		case <-c.ctx.Done():
+			return c.ctx.Err()
+		default:
+		}
+	}
+
+	childFiles := make([]*os.File, 0, 3+len(c.ExtraFiles))
+	stdin, err := c.childStdin()
+	if err != nil {
+		return err
+	}
+	childFiles = append(childFiles, stdin)
+	stdout, err := c.childStdout()
+	if err != nil {
+		return err
+	}
+	childFiles = append(childFiles, stdout)
+	stderr, err := c.childStderr(stdout)
+	if err != nil {
+		return err
+	}
+	childFiles = append(childFiles, stderr)
+	childFiles = append(childFiles, c.ExtraFiles...)
+
+	env, err := c.environ()
+	if err != nil {
+		return err
+	}
+
+	c.Process, err = os.StartProcess(lp, c.argv(), &os.ProcAttr{
+		Dir:   c.Dir,
+		Files: childFiles,
+		Env:   env,
+		Sys:   c.SysProcAttr,
+	})
+	if err != nil {
+		return err
+	}
+	started = true
+
+	// Don't allocate the goroutineErr channel unless there are goroutines to start.
+	if len(c.goroutine) > 0 {
+		goroutineErr := make(chan error, 1)
+		c.goroutineErr = goroutineErr
+
+		type goroutineStatus struct {
+			running  int
+			firstErr error
+		}
+		statusc := make(chan goroutineStatus, 1)
+		statusc <- goroutineStatus{running: len(c.goroutine)}
+		for _, fn := range c.goroutine {
+			go func(fn func() error) {
+				err := fn()
+
+				status := <-statusc
+				if status.firstErr == nil {
+					status.firstErr = err
+				}
+				status.running--
+				if status.running == 0 {
+					goroutineErr <- status.firstErr
+				} else {
+					statusc <- status
+				}
+			}(fn)
+		}
+		c.goroutine = nil // Allow the goroutines' closures to be GC'd when they complete.
+	}
+
+	// If we have anything to do when the command's Context expires,
+	// start a goroutine to watch for cancellation.
+	//
+	// (Even if the command was created by CommandContext, a helper library may
+	// have explicitly set its Cancel field back to nil, indicating that it should
+	// be allowed to continue running after cancellation after all.)
+	if (c.Cancel != nil || c.WaitDelay != 0) && c.ctx != nil && c.ctx.Done() != nil {
+		resultc := make(chan ctxResult)
+		c.ctxResult = resultc
+		go c.watchCtx(resultc)
+	}
+
+	return nil
+}
+
+// watchCtx watches c.ctx until it is able to send a result to resultc.
+//
+// If c.ctx is done before a result can be sent, watchCtx calls c.Cancel,
+// and/or kills cmd.Process it after c.WaitDelay has elapsed.
+//
+// watchCtx manipulates c.goroutineErr, so its result must be received before
+// c.awaitGoroutines is called.
+func (c *Cmd) watchCtx(resultc chan<- ctxResult) {
+	select {
+	case resultc <- ctxResult{}:
+		return
+	case <-c.ctx.Done():
+	}
+
+	var err error
+	if c.Cancel != nil {
+		if interruptErr := c.Cancel(); interruptErr == nil {
+			// We appear to have successfully interrupted the command, so any
+			// program behavior from this point may be due to ctx even if the
+			// command exits with code 0.
+			err = c.ctx.Err()
+		} else if errors.Is(interruptErr, os.ErrProcessDone) {
+			// The process already finished: we just didn't notice it yet.
+			// (Perhaps c.Wait hadn't been called, or perhaps it happened to race with
+			// c.ctx being cancelled.) Don't inject a needless error.
+		} else {
+			err = wrappedError{
+				prefix: "exec: canceling Cmd",
+				err:    interruptErr,
+			}
+		}
+	}
+	if c.WaitDelay == 0 {
+		resultc <- ctxResult{err: err}
+		return
+	}
+
+	timer := time.NewTimer(c.WaitDelay)
+	select {
+	case resultc <- ctxResult{err: err, timer: timer}:
+		// c.Process.Wait returned and we've handed the timer off to c.Wait.
+		// It will take care of goroutine shutdown from here.
+		return
+	case <-timer.C:
+	}
+
+	killed := false
+	if killErr := c.Process.Kill(); killErr == nil {
+		// We appear to have killed the process. c.Process.Wait should return a
+		// non-nil error to c.Wait unless the Kill signal races with a successful
+		// exit, and if that does happen we shouldn't report a spurious error,
+		// so don't set err to anything here.
+		killed = true
+	} else if !errors.Is(killErr, os.ErrProcessDone) {
+		err = wrappedError{
+			prefix: "exec: killing Cmd",
+			err:    killErr,
+		}
+	}
+
+	if c.goroutineErr != nil {
+		select {
+		case goroutineErr := <-c.goroutineErr:
+			// Forward goroutineErr only if we don't have reason to believe it was
+			// caused by a call to Cancel or Kill above.
+			if err == nil && !killed {
+				err = goroutineErr
+			}
+		default:
+			// Close the child process's I/O pipes, in case it abandoned some
+			// subprocess that inherited them and is still holding them open
+			// (see https://go.dev/issue/23019).
+			//
+			// We close the goroutine pipes only after we have sent any signals we're
+			// going to send to the process (via Signal or Kill above): if we send
+			// SIGKILL to the process, we would prefer for it to die of SIGKILL, not
+			// SIGPIPE. (However, this may still cause any orphaned subprocesses to
+			// terminate with SIGPIPE.)
+			closeDescriptors(c.parentIOPipes)
+			// Wait for the copying goroutines to finish, but report ErrWaitDelay for
+			// the error: any other error here could result from closing the pipes.
+			_ = <-c.goroutineErr
+			if err == nil {
+				err = ErrWaitDelay
+			}
+		}
+
+		// Since we have already received the only result from c.goroutineErr,
+		// set it to nil to prevent awaitGoroutines from blocking on it.
+		c.goroutineErr = nil
+	}
+
+	resultc <- ctxResult{err: err}
+}
+
+// An ExitError reports an unsuccessful exit by a command.
+type ExitError struct {
+	*os.ProcessState
+
+	// Stderr holds a subset of the standard error output from the
+	// Cmd.Output method if standard error was not otherwise being
+	// collected.
+	//
+	// If the error output is long, Stderr may contain only a prefix
+	// and suffix of the output, with the middle replaced with
+	// text about the number of omitted bytes.
+	//
+	// Stderr is provided for debugging, for inclusion in error messages.
+	// Users with other needs should redirect Cmd.Stderr as needed.
+	Stderr []byte
+}
+
+func (e *ExitError) Error() string {
+	return e.ProcessState.String()
+}
+
+// Wait waits for the command to exit and waits for any copying to
+// stdin or copying from stdout or stderr to complete.
+//
+// The command must have been started by Start.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *ExitError. Other error types may be
+// returned for I/O problems.
+//
+// If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits
+// for the respective I/O loop copying to or from the process to complete.
+//
+// Wait releases any resources associated with the Cmd.
+func (c *Cmd) Wait() error {
+	if c.Process == nil {
+		return errors.New("exec: not started")
+	}
+	if c.ProcessState != nil {
+		return errors.New("exec: Wait was already called")
+	}
+
+	state, err := c.Process.Wait()
+	if err == nil && !state.Success() {
+		err = &ExitError{ProcessState: state}
+	}
+	c.ProcessState = state
+
+	var timer *time.Timer
+	if c.ctxResult != nil {
+		watch := <-c.ctxResult
+		timer = watch.timer
+		// If c.Process.Wait returned an error, prefer that.
+		// Otherwise, report any error from the watchCtx goroutine,
+		// such as a Context cancellation or a WaitDelay overrun.
+		if err == nil && watch.err != nil {
+			err = watch.err
+		}
+	}
+
+	if goroutineErr := c.awaitGoroutines(timer); err == nil {
+		// Report an error from the copying goroutines only if the program otherwise
+		// exited normally on its own. Otherwise, the copying error may be due to the
+		// abnormal termination.
+		err = goroutineErr
+	}
+	closeDescriptors(c.parentIOPipes)
+	c.parentIOPipes = nil
+
+	return err
+}
+
+// awaitGoroutines waits for the results of the goroutines copying data to or
+// from the command's I/O pipes.
+//
+// If c.WaitDelay elapses before the goroutines complete, awaitGoroutines
+// forcibly closes their pipes and returns ErrWaitDelay.
+//
+// If timer is non-nil, it must send to timer.C at the end of c.WaitDelay.
+func (c *Cmd) awaitGoroutines(timer *time.Timer) error {
+	defer func() {
+		if timer != nil {
+			timer.Stop()
+		}
+		c.goroutineErr = nil
+	}()
+
+	if c.goroutineErr == nil {
+		return nil // No running goroutines to await.
+	}
+
+	if timer == nil {
+		if c.WaitDelay == 0 {
+			return <-c.goroutineErr
+		}
+
+		select {
+		case err := <-c.goroutineErr:
+			// Avoid the overhead of starting a timer.
+			return err
+		default:
+		}
+
+		// No existing timer was started: either there is no Context associated with
+		// the command, or c.Process.Wait completed before the Context was done.
+		timer = time.NewTimer(c.WaitDelay)
+	}
+
+	select {
+	case <-timer.C:
+		closeDescriptors(c.parentIOPipes)
+		// Wait for the copying goroutines to finish, but ignore any error
+		// (since it was probably caused by closing the pipes).
+		_ = <-c.goroutineErr
+		return ErrWaitDelay
+
+	case err := <-c.goroutineErr:
+		return err
+	}
+}
+
+// Output runs the command and returns its standard output.
+// Any returned error will usually be of type *ExitError.
+// If c.Stderr was nil, Output populates ExitError.Stderr.
+func (c *Cmd) Output() ([]byte, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	var stdout bytes.Buffer
+	c.Stdout = &stdout
+
+	captureErr := c.Stderr == nil
+	if captureErr {
+		c.Stderr = &prefixSuffixSaver{N: 32 << 10}
+	}
+
+	err := c.Run()
+	if err != nil && captureErr {
+		if ee, ok := err.(*ExitError); ok {
+			ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
+		}
+	}
+	return stdout.Bytes(), err
+}
+
+// CombinedOutput runs the command and returns its combined standard
+// output and standard error.
+func (c *Cmd) CombinedOutput() ([]byte, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	if c.Stderr != nil {
+		return nil, errors.New("exec: Stderr already set")
+	}
+	var b bytes.Buffer
+	c.Stdout = &b
+	c.Stderr = &b
+	err := c.Run()
+	return b.Bytes(), err
+}
+
+// StdinPipe returns a pipe that will be connected to the command's
+// standard input when the command starts.
+// The pipe will be closed automatically after Wait sees the command exit.
+// A caller need only call Close to force the pipe to close sooner.
+// For example, if the command being run will not exit until standard input
+// is closed, the caller must close the pipe.
+func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
+	if c.Stdin != nil {
+		return nil, errors.New("exec: Stdin already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StdinPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stdin = pr
+	c.childIOFiles = append(c.childIOFiles, pr)
+	c.parentIOPipes = append(c.parentIOPipes, pw)
+	return pw, nil
+}
+
+// StdoutPipe returns a pipe that will be connected to the command's
+// standard output when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves. It is thus incorrect to call Wait
+// before all reads from the pipe have completed.
+// For the same reason, it is incorrect to call Run when using StdoutPipe.
+// See the example for idiomatic usage.
+func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
+	if c.Stdout != nil {
+		return nil, errors.New("exec: Stdout already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StdoutPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stdout = pw
+	c.childIOFiles = append(c.childIOFiles, pw)
+	c.parentIOPipes = append(c.parentIOPipes, pr)
+	return pr, nil
+}
+
+// StderrPipe returns a pipe that will be connected to the command's
+// standard error when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves. It is thus incorrect to call Wait
+// before all reads from the pipe have completed.
+// For the same reason, it is incorrect to use Run when using StderrPipe.
+// See the StdoutPipe example for idiomatic usage.
+func (c *Cmd) StderrPipe() (io.ReadCloser, error) {
+	if c.Stderr != nil {
+		return nil, errors.New("exec: Stderr already set")
+	}
+	if c.Process != nil {
+		return nil, errors.New("exec: StderrPipe after process started")
+	}
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	c.Stderr = pw
+	c.childIOFiles = append(c.childIOFiles, pw)
+	c.parentIOPipes = append(c.parentIOPipes, pr)
+	return pr, nil
+}
+
+// prefixSuffixSaver is an io.Writer which retains the first N bytes
+// and the last N bytes written to it. The Bytes() methods reconstructs
+// it with a pretty error message.
+type prefixSuffixSaver struct {
+	N         int // max size of prefix or suffix
+	prefix    []byte
+	suffix    []byte // ring buffer once len(suffix) == N
+	suffixOff int    // offset to write into suffix
+	skipped   int64
+
+	// TODO(bradfitz): we could keep one large []byte and use part of it for
+	// the prefix, reserve space for the '... Omitting N bytes ...' message,
+	// then the ring buffer suffix, and just rearrange the ring buffer
+	// suffix when Bytes() is called, but it doesn't seem worth it for
+	// now just for error messages. It's only ~64KB anyway.
+}
+
+func (w *prefixSuffixSaver) Write(p []byte) (n int, err error) {
+	lenp := len(p)
+	p = w.fill(&w.prefix, p)
+
+	// Only keep the last w.N bytes of suffix data.
+	if overage := len(p) - w.N; overage > 0 {
+		p = p[overage:]
+		w.skipped += int64(overage)
+	}
+	p = w.fill(&w.suffix, p)
+
+	// w.suffix is full now if p is non-empty. Overwrite it in a circle.
+	for len(p) > 0 { // 0, 1, or 2 iterations.
+		n := copy(w.suffix[w.suffixOff:], p)
+		p = p[n:]
+		w.skipped += int64(n)
+		w.suffixOff += n
+		if w.suffixOff == w.N {
+			w.suffixOff = 0
+		}
+	}
+	return lenp, nil
+}
+
+// fill appends up to len(p) bytes of p to *dst, such that *dst does not
+// grow larger than w.N. It returns the un-appended suffix of p.
+func (w *prefixSuffixSaver) fill(dst *[]byte, p []byte) (pRemain []byte) {
+	if remain := w.N - len(*dst); remain > 0 {
+		add := min(len(p), remain)
+		*dst = append(*dst, p[:add]...)
+		p = p[add:]
+	}
+	return p
+}
+
+func (w *prefixSuffixSaver) Bytes() []byte {
+	if w.suffix == nil {
+		return w.prefix
+	}
+	if w.skipped == 0 {
+		return append(w.prefix, w.suffix...)
+	}
+	var buf bytes.Buffer
+	buf.Grow(len(w.prefix) + len(w.suffix) + 50)
+	buf.Write(w.prefix)
+	buf.WriteString("\n... omitting ")
+	buf.WriteString(strconv.FormatInt(w.skipped, 10))
+	buf.WriteString(" bytes ...\n")
+	buf.Write(w.suffix[w.suffixOff:])
+	buf.Write(w.suffix[:w.suffixOff])
+	return buf.Bytes()
+}
+
+// environ returns a best-effort copy of the environment in which the command
+// would be run as it is currently configured. If an error occurs in computing
+// the environment, it is returned alongside the best-effort copy.
+func (c *Cmd) environ() ([]string, error) {
+	var err error
+
+	env := c.Env
+	if env == nil {
+		env, err = execenv.Default(c.SysProcAttr)
+		if err != nil {
+			env = os.Environ()
+			// Note that the non-nil err is preserved despite env being overridden.
+		}
+
+		if c.Dir != "" {
+			switch runtime.GOOS {
+			case "windows", "plan9":
+				// Windows and Plan 9 do not use the PWD variable, so we don't need to
+				// keep it accurate.
+			default:
+				// On POSIX platforms, PWD represents “an absolute pathname of the
+				// current working directory.” Since we are changing the working
+				// directory for the command, we should also update PWD to reflect that.
+				//
+				// Unfortunately, we didn't always do that, so (as proposed in
+				// https://go.dev/issue/50599) to avoid unintended collateral damage we
+				// only implicitly update PWD when Env is nil. That way, we're much
+				// less likely to override an intentional change to the variable.
+				if pwd, absErr := filepath.Abs(c.Dir); absErr == nil {
+					env = append(env, "PWD="+pwd)
+				} else if err == nil {
+					err = absErr
+				}
+			}
+		}
+	}
+
+	env, dedupErr := dedupEnv(env)
+	if err == nil {
+		err = dedupErr
+	}
+	return addCriticalEnv(env), err
+}
+
+// Environ returns a copy of the environment in which the command would be run
+// as it is currently configured.
+func (c *Cmd) Environ() []string {
+	//  Intentionally ignore errors: environ returns a best-effort environment no matter what.
+	env, _ := c.environ()
+	return env
+}
+
+// dedupEnv returns a copy of env with any duplicates removed, in favor of
+// later values.
+// Items not of the normal environment "key=value" form are preserved unchanged.
+// Except on Plan 9, items containing NUL characters are removed, and
+// an error is returned along with the remaining values.
+func dedupEnv(env []string) ([]string, error) {
+	return dedupEnvCase(runtime.GOOS == "windows", runtime.GOOS == "plan9", env)
+}
+
+// dedupEnvCase is dedupEnv with a case option for testing.
+// If caseInsensitive is true, the case of keys is ignored.
+// If nulOK is false, items containing NUL characters are allowed.
+func dedupEnvCase(caseInsensitive, nulOK bool, env []string) ([]string, error) {
+	// Construct the output in reverse order, to preserve the
+	// last occurrence of each key.
+	var err error
+	out := make([]string, 0, len(env))
+	saw := make(map[string]bool, len(env))
+	for n := len(env); n > 0; n-- {
+		kv := env[n-1]
+
+		// Reject NUL in environment variables to prevent security issues (#56284);
+		// except on Plan 9, which uses NUL as os.PathListSeparator (#56544).
+		if !nulOK && strings.IndexByte(kv, 0) != -1 {
+			err = errors.New("exec: environment variable contains NUL")
+			continue
+		}
+
+		i := strings.Index(kv, "=")
+		if i == 0 {
+			// We observe in practice keys with a single leading "=" on Windows.
+			// TODO(#49886): Should we consume only the first leading "=" as part
+			// of the key, or parse through arbitrarily many of them until a non-"="?
+			i = strings.Index(kv[1:], "=") + 1
+		}
+		if i < 0 {
+			if kv != "" {
+				// The entry is not of the form "key=value" (as it is required to be).
+				// Leave it as-is for now.
+				// TODO(#52436): should we strip or reject these bogus entries?
+				out = append(out, kv)
+			}
+			continue
+		}
+		k := kv[:i]
+		if caseInsensitive {
+			k = strings.ToLower(k)
+		}
+		if saw[k] {
+			continue
+		}
+
+		saw[k] = true
+		out = append(out, kv)
+	}
+
+	// Now reverse the slice to restore the original order.
+	for i := 0; i < len(out)/2; i++ {
+		j := len(out) - i - 1
+		out[i], out[j] = out[j], out[i]
+	}
+
+	return out, err
+}
+
+// addCriticalEnv adds any critical environment variables that are required
+// (or at least almost always required) on the operating system.
+// Currently this is only used for Windows.
+func addCriticalEnv(env []string) []string {
+	if runtime.GOOS != "windows" {
+		return env
+	}
+	for _, kv := range env {
+		k, _, ok := strings.Cut(kv, "=")
+		if !ok {
+			continue
+		}
+		if strings.EqualFold(k, "SYSTEMROOT") {
+			// We already have it.
+			return env
+		}
+	}
+	return append(env, "SYSTEMROOT="+os.Getenv("SYSTEMROOT"))
+}
+
+// ErrDot indicates that a path lookup resolved to an executable
+// in the current directory due to ‘.’ being in the path, either
+// implicitly or explicitly. See the package documentation for details.
+//
+// Note that functions in this package do not return ErrDot directly.
+// Code should use errors.Is(err, ErrDot), not err == ErrDot,
+// to test whether a returned error err is due to this condition.
+var ErrDot = errors.New("cannot run executable found relative to current directory")
diff --git a/src/os/exec/exec_linux_test.go b/src/os/exec/exec_linux_test.go
new file mode 100644
index 0000000..b9f6b7b
--- /dev/null
+++ b/src/os/exec/exec_linux_test.go
@@ -0,0 +1,45 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && cgo
+
+// On systems that use glibc, calling malloc can create a new arena,
+// and creating a new arena can read /sys/devices/system/cpu/online.
+// If we are using cgo, we will call malloc when creating a new thread.
+// That can break TestExtraFiles if we create a new thread that creates
+// a new arena and opens the /sys file while we are checking for open
+// file descriptors. Work around the problem by creating threads up front.
+// See issue 25628.
+
+package exec_test
+
+import (
+	"os"
+	"sync"
+	"syscall"
+	"time"
+)
+
+func init() {
+	if os.Getenv("GO_EXEC_TEST_PID") == "" {
+		return
+	}
+
+	// Start some threads. 10 is arbitrary but intended to be enough
+	// to ensure that the code won't have to create any threads itself.
+	// In particular this should be more than the number of threads
+	// the garbage collector might create.
+	const threads = 10
+
+	var wg sync.WaitGroup
+	wg.Add(threads)
+	ts := syscall.NsecToTimespec((100 * time.Microsecond).Nanoseconds())
+	for i := 0; i < threads; i++ {
+		go func() {
+			defer wg.Done()
+			syscall.Nanosleep(&ts, nil)
+		}()
+	}
+	wg.Wait()
+}
diff --git a/src/os/exec/exec_other_test.go b/src/os/exec/exec_other_test.go
new file mode 100644
index 0000000..64c819c
--- /dev/null
+++ b/src/os/exec/exec_other_test.go
@@ -0,0 +1,14 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !unix && !windows
+
+package exec_test
+
+import "os"
+
+var (
+	quitSignal os.Signal = nil
+	pipeSignal os.Signal = nil
+)
diff --git a/src/os/exec/exec_plan9.go b/src/os/exec/exec_plan9.go
new file mode 100644
index 0000000..8920bec
--- /dev/null
+++ b/src/os/exec/exec_plan9.go
@@ -0,0 +1,19 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import "io/fs"
+
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore hungup errors copying to stdin if the program
+	// completed successfully otherwise.
+	// See Issue 35753.
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		pe.Err.Error() == "i/o on hungup channel"
+}
diff --git a/src/os/exec/exec_posix_test.go b/src/os/exec/exec_posix_test.go
new file mode 100644
index 0000000..5d828b3
--- /dev/null
+++ b/src/os/exec/exec_posix_test.go
@@ -0,0 +1,276 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package exec_test
+
+import (
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"os/user"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func init() {
+	registerHelperCommand("pwd", cmdPwd)
+}
+
+func cmdPwd(...string) {
+	pwd, err := os.Getwd()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	fmt.Println(pwd)
+}
+
+func TestCredentialNoSetGroups(t *testing.T) {
+	if runtime.GOOS == "android" {
+		maySkipHelperCommand("echo")
+		t.Skip("unsupported on Android")
+	}
+	t.Parallel()
+
+	u, err := user.Current()
+	if err != nil {
+		t.Fatalf("error getting current user: %v", err)
+	}
+
+	uid, err := strconv.Atoi(u.Uid)
+	if err != nil {
+		t.Fatalf("error converting Uid=%s to integer: %v", u.Uid, err)
+	}
+
+	gid, err := strconv.Atoi(u.Gid)
+	if err != nil {
+		t.Fatalf("error converting Gid=%s to integer: %v", u.Gid, err)
+	}
+
+	// If NoSetGroups is true, setgroups isn't called and cmd.Run should succeed
+	cmd := helperCommand(t, "echo", "foo")
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Credential: &syscall.Credential{
+			Uid:         uint32(uid),
+			Gid:         uint32(gid),
+			NoSetGroups: true,
+		},
+	}
+
+	if err = cmd.Run(); err != nil {
+		t.Errorf("Failed to run command: %v", err)
+	}
+}
+
+// For issue #19314: make sure that SIGSTOP does not cause the process
+// to appear done.
+func TestWaitid(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "pipetest")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Wait for the child process to come up and register any signal handlers.
+	const msg = "O:ping\n"
+	if _, err := io.WriteString(stdin, msg); err != nil {
+		t.Fatal(err)
+	}
+	buf := make([]byte, len(msg))
+	if _, err := io.ReadFull(stdout, buf); err != nil {
+		t.Fatal(err)
+	}
+	// Now leave the pipes open so that the process will hang until we close stdin.
+
+	if err := cmd.Process.Signal(syscall.SIGSTOP); err != nil {
+		cmd.Process.Kill()
+		t.Fatal(err)
+	}
+
+	ch := make(chan error)
+	go func() {
+		ch <- cmd.Wait()
+	}()
+
+	// Give a little time for Wait to block on waiting for the process.
+	// (This is just to give some time to trigger the bug; it should not be
+	// necessary for the test to pass.)
+	if testing.Short() {
+		time.Sleep(1 * time.Millisecond)
+	} else {
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	// This call to Signal should succeed because the process still exists.
+	// (Prior to the fix for #19314, this would fail with os.ErrProcessDone
+	// or an equivalent error.)
+	if err := cmd.Process.Signal(syscall.SIGCONT); err != nil {
+		t.Error(err)
+		syscall.Kill(cmd.Process.Pid, syscall.SIGCONT)
+	}
+
+	// The SIGCONT should allow the process to wake up, notice that stdin
+	// is closed, and exit successfully.
+	stdin.Close()
+	err = <-ch
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// https://go.dev/issue/50599: if Env is not set explicitly, setting Dir should
+// implicitly update PWD to the correct path, and Environ should list the
+// updated value.
+func TestImplicitPWD(t *testing.T) {
+	t.Parallel()
+
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cases := []struct {
+		name string
+		dir  string
+		want string
+	}{
+		{"empty", "", cwd},
+		{"dot", ".", cwd},
+		{"dotdot", "..", filepath.Dir(cwd)},
+		{"PWD", cwd, cwd},
+		{"PWDdotdot", cwd + string(filepath.Separator) + "..", filepath.Dir(cwd)},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			cmd := helperCommand(t, "pwd")
+			if cmd.Env != nil {
+				t.Fatalf("test requires helperCommand not to set Env field")
+			}
+			cmd.Dir = tc.dir
+
+			var pwds []string
+			for _, kv := range cmd.Environ() {
+				if strings.HasPrefix(kv, "PWD=") {
+					pwds = append(pwds, strings.TrimPrefix(kv, "PWD="))
+				}
+			}
+
+			wantPWDs := []string{tc.want}
+			if tc.dir == "" {
+				if _, ok := os.LookupEnv("PWD"); !ok {
+					wantPWDs = nil
+				}
+			}
+			if !reflect.DeepEqual(pwds, wantPWDs) {
+				t.Errorf("PWD entries in cmd.Environ():\n\t%s\nwant:\n\t%s", strings.Join(pwds, "\n\t"), strings.Join(wantPWDs, "\n\t"))
+			}
+
+			cmd.Stderr = new(strings.Builder)
+			out, err := cmd.Output()
+			if err != nil {
+				t.Fatalf("%v:\n%s", err, cmd.Stderr)
+			}
+			got := strings.Trim(string(out), "\r\n")
+			t.Logf("in\n\t%s\n`pwd` reported\n\t%s", tc.dir, got)
+			if got != tc.want {
+				t.Errorf("want\n\t%s", tc.want)
+			}
+		})
+	}
+}
+
+// However, if cmd.Env is set explicitly, setting Dir should not override it.
+// (This checks that the implementation for https://go.dev/issue/50599 doesn't
+// break existing users who may have explicitly mismatched the PWD variable.)
+func TestExplicitPWD(t *testing.T) {
+	t.Parallel()
+
+	maySkipHelperCommand("pwd")
+	testenv.MustHaveSymlink(t)
+
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	link := filepath.Join(t.TempDir(), "link")
+	if err := os.Symlink(cwd, link); err != nil {
+		t.Fatal(err)
+	}
+
+	// Now link is another equally-valid name for cwd. If we set Dir to one and
+	// PWD to the other, the subprocess should report the PWD version.
+	cases := []struct {
+		name string
+		dir  string
+		pwd  string
+	}{
+		{name: "original PWD", pwd: cwd},
+		{name: "link PWD", pwd: link},
+		{name: "in link with original PWD", dir: link, pwd: cwd},
+		{name: "in dir with link PWD", dir: cwd, pwd: link},
+		// Ideally we would also like to test what happens if we set PWD to
+		// something totally bogus (or the empty string), but then we would have no
+		// idea what output the subprocess should actually produce: cwd itself may
+		// contain symlinks preserved from the PWD value in the test's environment.
+	}
+	for _, tc := range cases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			cmd := helperCommand(t, "pwd")
+			// This is intentionally opposite to the usual order of setting cmd.Dir
+			// and then calling cmd.Environ. Here, we *want* PWD not to match cmd.Dir,
+			// so we don't care whether cmd.Dir is reflected in cmd.Environ.
+			cmd.Env = append(cmd.Environ(), "PWD="+tc.pwd)
+			cmd.Dir = tc.dir
+
+			var pwds []string
+			for _, kv := range cmd.Environ() {
+				if strings.HasPrefix(kv, "PWD=") {
+					pwds = append(pwds, strings.TrimPrefix(kv, "PWD="))
+				}
+			}
+
+			wantPWDs := []string{tc.pwd}
+			if !reflect.DeepEqual(pwds, wantPWDs) {
+				t.Errorf("PWD entries in cmd.Environ():\n\t%s\nwant:\n\t%s", strings.Join(pwds, "\n\t"), strings.Join(wantPWDs, "\n\t"))
+			}
+
+			cmd.Stderr = new(strings.Builder)
+			out, err := cmd.Output()
+			if err != nil {
+				t.Fatalf("%v:\n%s", err, cmd.Stderr)
+			}
+			got := strings.Trim(string(out), "\r\n")
+			t.Logf("in\n\t%s\nwith PWD=%s\nsubprocess os.Getwd() reported\n\t%s", tc.dir, tc.pwd, got)
+			if got != tc.pwd {
+				t.Errorf("want\n\t%s", tc.pwd)
+			}
+		})
+	}
+}
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
new file mode 100644
index 0000000..71a0049
--- /dev/null
+++ b/src/os/exec/exec_test.go
@@ -0,0 +1,1837 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Use an external test to avoid os/exec -> net/http -> crypto/x509 -> os/exec
+// circular dependency on non-cgo darwin.
+
+package exec_test
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"internal/poll"
+	"internal/testenv"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"os/exec/internal/fdtest"
+	"os/signal"
+	"path/filepath"
+	"runtime"
+	"runtime/debug"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// haveUnexpectedFDs is set at init time to report whether any file descriptors
+// were open at program start.
+var haveUnexpectedFDs bool
+
+func init() {
+	godebug := os.Getenv("GODEBUG")
+	if godebug != "" {
+		godebug += ","
+	}
+	godebug += "execwait=2"
+	os.Setenv("GODEBUG", godebug)
+
+	if os.Getenv("GO_EXEC_TEST_PID") != "" {
+		return
+	}
+	if runtime.GOOS == "windows" {
+		return
+	}
+	for fd := uintptr(3); fd <= 100; fd++ {
+		if poll.IsPollDescriptor(fd) {
+			continue
+		}
+
+		if fdtest.Exists(fd) {
+			haveUnexpectedFDs = true
+			return
+		}
+	}
+}
+
+// TestMain allows the test binary to impersonate many other binaries,
+// some of which may manipulate os.Stdin, os.Stdout, and/or os.Stderr
+// (and thus cannot run as an ordinary Test function, since the testing
+// package monkey-patches those variables before running tests).
+func TestMain(m *testing.M) {
+	flag.Parse()
+
+	pid := os.Getpid()
+	if os.Getenv("GO_EXEC_TEST_PID") == "" {
+		os.Setenv("GO_EXEC_TEST_PID", strconv.Itoa(pid))
+
+		if runtime.GOOS == "windows" {
+			// Normalize environment so that test behavior is consistent.
+			// (The behavior of LookPath varies depending on this variable.)
+			//
+			// Ideally we would test both with the variable set and with it cleared,
+			// but I (bcmills) am not sure that that's feasible: it may already be set
+			// in the Windows registry, and I'm not sure if it is possible to remove
+			// a registry variable in a program's environment.
+			//
+			// Per https://learn.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-needcurrentdirectoryforexepathw#remarks,
+			// “the existence of the NoDefaultCurrentDirectoryInExePath environment
+			// variable is checked, and not its value.”
+			os.Setenv("NoDefaultCurrentDirectoryInExePath", "TRUE")
+		}
+
+		code := m.Run()
+		if code == 0 && flag.Lookup("test.run").Value.String() == "" && flag.Lookup("test.list").Value.String() == "" {
+			for cmd := range helperCommands {
+				if _, ok := helperCommandUsed.Load(cmd); !ok {
+					fmt.Fprintf(os.Stderr, "helper command unused: %q\n", cmd)
+					code = 1
+				}
+			}
+		}
+
+		if !testing.Short() {
+			// Run a couple of GC cycles to increase the odds of detecting
+			// process leaks using the finalizers installed by GODEBUG=execwait=2.
+			runtime.GC()
+			runtime.GC()
+		}
+
+		os.Exit(code)
+	}
+
+	args := flag.Args()
+	if len(args) == 0 {
+		fmt.Fprintf(os.Stderr, "No command\n")
+		os.Exit(2)
+	}
+
+	cmd, args := args[0], args[1:]
+	f, ok := helperCommands[cmd]
+	if !ok {
+		fmt.Fprintf(os.Stderr, "Unknown command %q\n", cmd)
+		os.Exit(2)
+	}
+	f(args...)
+	os.Exit(0)
+}
+
+// registerHelperCommand registers a command that the test process can impersonate.
+// A command should be registered in the same source file in which it is used.
+// If all tests are run and pass, all registered commands must be used.
+// (This prevents stale commands from accreting if tests are removed or
+// refactored over time.)
+func registerHelperCommand(name string, f func(...string)) {
+	if helperCommands[name] != nil {
+		panic("duplicate command registered: " + name)
+	}
+	helperCommands[name] = f
+}
+
+// maySkipHelperCommand records that the test that uses the named helper command
+// was invoked, but may call Skip on the test before actually calling
+// helperCommand.
+func maySkipHelperCommand(name string) {
+	helperCommandUsed.Store(name, true)
+}
+
+// helperCommand returns an exec.Cmd that will run the named helper command.
+func helperCommand(t *testing.T, name string, args ...string) *exec.Cmd {
+	t.Helper()
+	return helperCommandContext(t, nil, name, args...)
+}
+
+// helperCommandContext is like helperCommand, but also accepts a Context under
+// which to run the command.
+func helperCommandContext(t *testing.T, ctx context.Context, name string, args ...string) (cmd *exec.Cmd) {
+	helperCommandUsed.LoadOrStore(name, true)
+
+	t.Helper()
+	testenv.MustHaveExec(t)
+
+	cs := append([]string{name}, args...)
+	if ctx != nil {
+		cmd = exec.CommandContext(ctx, exePath(t), cs...)
+	} else {
+		cmd = exec.Command(exePath(t), cs...)
+	}
+	return cmd
+}
+
+// exePath returns the path to the running executable.
+func exePath(t testing.TB) string {
+	exeOnce.Do(func() {
+		// Use os.Executable instead of os.Args[0] in case the caller modifies
+		// cmd.Dir: if the test binary is invoked like "./exec.test", it should
+		// not fail spuriously.
+		exeOnce.path, exeOnce.err = os.Executable()
+	})
+
+	if exeOnce.err != nil {
+		if t == nil {
+			panic(exeOnce.err)
+		}
+		t.Fatal(exeOnce.err)
+	}
+
+	return exeOnce.path
+}
+
+var exeOnce struct {
+	path string
+	err  error
+	sync.Once
+}
+
+func chdir(t *testing.T, dir string) {
+	t.Helper()
+
+	prev, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Chdir(%#q)", dir)
+
+	t.Cleanup(func() {
+		if err := os.Chdir(prev); err != nil {
+			// Couldn't chdir back to the original working directory.
+			// panic instead of t.Fatal so that we don't run other tests
+			// in an unexpected location.
+			panic("couldn't restore working directory: " + err.Error())
+		}
+	})
+}
+
+var helperCommandUsed sync.Map
+
+var helperCommands = map[string]func(...string){
+	"echo":          cmdEcho,
+	"echoenv":       cmdEchoEnv,
+	"cat":           cmdCat,
+	"pipetest":      cmdPipeTest,
+	"stdinClose":    cmdStdinClose,
+	"exit":          cmdExit,
+	"describefiles": cmdDescribeFiles,
+	"stderrfail":    cmdStderrFail,
+	"yes":           cmdYes,
+	"hang":          cmdHang,
+}
+
+func cmdEcho(args ...string) {
+	iargs := []any{}
+	for _, s := range args {
+		iargs = append(iargs, s)
+	}
+	fmt.Println(iargs...)
+}
+
+func cmdEchoEnv(args ...string) {
+	for _, s := range args {
+		fmt.Println(os.Getenv(s))
+	}
+}
+
+func cmdCat(args ...string) {
+	if len(args) == 0 {
+		io.Copy(os.Stdout, os.Stdin)
+		return
+	}
+	exit := 0
+	for _, fn := range args {
+		f, err := os.Open(fn)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			exit = 2
+		} else {
+			defer f.Close()
+			io.Copy(os.Stdout, f)
+		}
+	}
+	os.Exit(exit)
+}
+
+func cmdPipeTest(...string) {
+	bufr := bufio.NewReader(os.Stdin)
+	for {
+		line, _, err := bufr.ReadLine()
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			os.Exit(1)
+		}
+		if bytes.HasPrefix(line, []byte("O:")) {
+			os.Stdout.Write(line)
+			os.Stdout.Write([]byte{'\n'})
+		} else if bytes.HasPrefix(line, []byte("E:")) {
+			os.Stderr.Write(line)
+			os.Stderr.Write([]byte{'\n'})
+		} else {
+			os.Exit(1)
+		}
+	}
+}
+
+func cmdStdinClose(...string) {
+	b, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
+	if s := string(b); s != stdinCloseTestString {
+		fmt.Fprintf(os.Stderr, "Error: Read %q, want %q", s, stdinCloseTestString)
+		os.Exit(1)
+	}
+}
+
+func cmdExit(args ...string) {
+	n, _ := strconv.Atoi(args[0])
+	os.Exit(n)
+}
+
+func cmdDescribeFiles(args ...string) {
+	f := os.NewFile(3, fmt.Sprintf("fd3"))
+	ln, err := net.FileListener(f)
+	if err == nil {
+		fmt.Printf("fd3: listener %s\n", ln.Addr())
+		ln.Close()
+	}
+}
+
+func cmdStderrFail(...string) {
+	fmt.Fprintf(os.Stderr, "some stderr text\n")
+	os.Exit(1)
+}
+
+func cmdYes(args ...string) {
+	if len(args) == 0 {
+		args = []string{"y"}
+	}
+	s := strings.Join(args, " ") + "\n"
+	for {
+		_, err := os.Stdout.WriteString(s)
+		if err != nil {
+			os.Exit(1)
+		}
+	}
+}
+
+func TestEcho(t *testing.T) {
+	t.Parallel()
+
+	bs, err := helperCommand(t, "echo", "foo bar", "baz").Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(bs), "foo bar baz\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCommandRelativeName(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "echo", "foo")
+
+	// Run our own binary as a relative path
+	// (e.g. "_test/exec.test") our parent directory.
+	base := filepath.Base(os.Args[0]) // "exec.test"
+	dir := filepath.Dir(os.Args[0])   // "/tmp/go-buildNNNN/os/exec/_test"
+	if dir == "." {
+		t.Skip("skipping; running test at root somehow")
+	}
+	parentDir := filepath.Dir(dir) // "/tmp/go-buildNNNN/os/exec"
+	dirBase := filepath.Base(dir)  // "_test"
+	if dirBase == "." {
+		t.Skipf("skipping; unexpected shallow dir of %q", dir)
+	}
+
+	cmd.Path = filepath.Join(dirBase, base)
+	cmd.Dir = parentDir
+
+	out, err := cmd.Output()
+	if err != nil {
+		t.Errorf("echo: %v", err)
+	}
+	if g, e := string(out), "foo\n"; g != e {
+		t.Errorf("echo: want %q, got %q", e, g)
+	}
+}
+
+func TestCatStdin(t *testing.T) {
+	t.Parallel()
+
+	// Cat, testing stdin and stdout.
+	input := "Input string\nLine 2"
+	p := helperCommand(t, "cat")
+	p.Stdin = strings.NewReader(input)
+	bs, err := p.Output()
+	if err != nil {
+		t.Errorf("cat: %v", err)
+	}
+	s := string(bs)
+	if s != input {
+		t.Errorf("cat: want %q, got %q", input, s)
+	}
+}
+
+func TestEchoFileRace(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "echo")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("StdinPipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+	wrote := make(chan bool)
+	go func() {
+		defer close(wrote)
+		fmt.Fprint(stdin, "echo\n")
+	}()
+	if err := cmd.Wait(); err != nil {
+		t.Fatalf("Wait: %v", err)
+	}
+	<-wrote
+}
+
+func TestCatGoodAndBadFile(t *testing.T) {
+	t.Parallel()
+
+	// Testing combined output and error values.
+	bs, err := helperCommand(t, "cat", "/bogus/file.foo", "exec_test.go").CombinedOutput()
+	if _, ok := err.(*exec.ExitError); !ok {
+		t.Errorf("expected *exec.ExitError from cat combined; got %T: %v", err, err)
+	}
+	errLine, body, ok := strings.Cut(string(bs), "\n")
+	if !ok {
+		t.Fatalf("expected two lines from cat; got %q", bs)
+	}
+	if !strings.HasPrefix(errLine, "Error: open /bogus/file.foo") {
+		t.Errorf("expected stderr to complain about file; got %q", errLine)
+	}
+	if !strings.Contains(body, "func TestCatGoodAndBadFile(t *testing.T)") {
+		t.Errorf("expected test code; got %q (len %d)", body, len(body))
+	}
+}
+
+func TestNoExistExecutable(t *testing.T) {
+	t.Parallel()
+
+	// Can't run a non-existent executable
+	err := exec.Command("/no-exist-executable").Run()
+	if err == nil {
+		t.Error("expected error from /no-exist-executable")
+	}
+}
+
+func TestExitStatus(t *testing.T) {
+	t.Parallel()
+
+	// Test that exit values are returned correctly
+	cmd := helperCommand(t, "exit", "42")
+	err := cmd.Run()
+	want := "exit status 42"
+	switch runtime.GOOS {
+	case "plan9":
+		want = fmt.Sprintf("exit status: '%s %d: 42'", filepath.Base(cmd.Path), cmd.ProcessState.Pid())
+	}
+	if werr, ok := err.(*exec.ExitError); ok {
+		if s := werr.Error(); s != want {
+			t.Errorf("from exit 42 got exit %q, want %q", s, want)
+		}
+	} else {
+		t.Fatalf("expected *exec.ExitError from exit 42; got %T: %v", err, err)
+	}
+}
+
+func TestExitCode(t *testing.T) {
+	t.Parallel()
+
+	// Test that exit code are returned correctly
+	cmd := helperCommand(t, "exit", "42")
+	cmd.Run()
+	want := 42
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got := cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "/no-exist-executable")
+	cmd.Run()
+	want = 2
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "exit", "255")
+	cmd.Run()
+	want = 255
+	if runtime.GOOS == "plan9" {
+		want = 1
+	}
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	cmd = helperCommand(t, "cat")
+	cmd.Run()
+	want = 0
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+
+	// Test when command does not call Run().
+	cmd = helperCommand(t, "cat")
+	want = -1
+	got = cmd.ProcessState.ExitCode()
+	if want != got {
+		t.Errorf("ExitCode got %d, want %d", got, want)
+	}
+}
+
+func TestPipes(t *testing.T) {
+	t.Parallel()
+
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	// Cat, testing stdin and stdout.
+	c := helperCommand(t, "pipetest")
+	stdin, err := c.StdinPipe()
+	check("StdinPipe", err)
+	stdout, err := c.StdoutPipe()
+	check("StdoutPipe", err)
+	stderr, err := c.StderrPipe()
+	check("StderrPipe", err)
+
+	outbr := bufio.NewReader(stdout)
+	errbr := bufio.NewReader(stderr)
+	line := func(what string, br *bufio.Reader) string {
+		line, _, err := br.ReadLine()
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+		return string(line)
+	}
+
+	err = c.Start()
+	check("Start", err)
+
+	_, err = stdin.Write([]byte("O:I am output\n"))
+	check("first stdin Write", err)
+	if g, e := line("first output line", outbr), "O:I am output"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("E:I am error\n"))
+	check("second stdin Write", err)
+	if g, e := line("first error line", errbr), "E:I am error"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	_, err = stdin.Write([]byte("O:I am output2\n"))
+	check("third stdin Write 3", err)
+	if g, e := line("second output line", outbr), "O:I am output2"; g != e {
+		t.Errorf("got %q, want %q", g, e)
+	}
+
+	stdin.Close()
+	err = c.Wait()
+	check("Wait", err)
+}
+
+const stdinCloseTestString = "Some test string."
+
+// Issue 6270.
+func TestStdinClose(t *testing.T) {
+	t.Parallel()
+
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	cmd := helperCommand(t, "stdinClose")
+	stdin, err := cmd.StdinPipe()
+	check("StdinPipe", err)
+	// Check that we can access methods of the underlying os.File.`
+	if _, ok := stdin.(interface {
+		Fd() uintptr
+	}); !ok {
+		t.Error("can't access methods of underlying *os.File")
+	}
+	check("Start", cmd.Start())
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	defer wg.Wait()
+	go func() {
+		defer wg.Done()
+
+		_, err := io.Copy(stdin, strings.NewReader(stdinCloseTestString))
+		check("Copy", err)
+
+		// Before the fix, this next line would race with cmd.Wait.
+		if err := stdin.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
+			t.Errorf("Close: %v", err)
+		}
+	}()
+
+	check("Wait", cmd.Wait())
+}
+
+// Issue 17647.
+// It used to be the case that TestStdinClose, above, would fail when
+// run under the race detector. This test is a variant of TestStdinClose
+// that also used to fail when run under the race detector.
+// This test is run by cmd/dist under the race detector to verify that
+// the race detector no longer reports any problems.
+func TestStdinCloseRace(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "stdinClose")
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("StdinPipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("Start: %v", err)
+
+	}
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+	defer wg.Wait()
+
+	go func() {
+		defer wg.Done()
+		// We don't check the error return of Kill. It is
+		// possible that the process has already exited, in
+		// which case Kill will return an error "process
+		// already finished". The purpose of this test is to
+		// see whether the race detector reports an error; it
+		// doesn't matter whether this Kill succeeds or not.
+		cmd.Process.Kill()
+	}()
+
+	go func() {
+		defer wg.Done()
+		// Send the wrong string, so that the child fails even
+		// if the other goroutine doesn't manage to kill it first.
+		// This test is to check that the race detector does not
+		// falsely report an error, so it doesn't matter how the
+		// child process fails.
+		io.Copy(stdin, strings.NewReader("unexpected string"))
+		if err := stdin.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
+			t.Errorf("stdin.Close: %v", err)
+		}
+	}()
+
+	if err := cmd.Wait(); err == nil {
+		t.Fatalf("Wait: succeeded unexpectedly")
+	}
+}
+
+// Issue 5071
+func TestPipeLookPathLeak(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("we don't currently suppore counting open handles on windows")
+	}
+	// Not parallel: checks for leaked file descriptors
+
+	openFDs := func() []uintptr {
+		var fds []uintptr
+		for i := uintptr(0); i < 100; i++ {
+			if fdtest.Exists(i) {
+				fds = append(fds, i)
+			}
+		}
+		return fds
+	}
+
+	old := map[uintptr]bool{}
+	for _, fd := range openFDs() {
+		old[fd] = true
+	}
+
+	for i := 0; i < 6; i++ {
+		cmd := exec.Command("something-that-does-not-exist-executable")
+		cmd.StdoutPipe()
+		cmd.StderrPipe()
+		cmd.StdinPipe()
+		if err := cmd.Run(); err == nil {
+			t.Fatal("unexpected success")
+		}
+	}
+
+	// Since this test is not running in parallel, we don't expect any new file
+	// descriptors to be opened while it runs. However, if there are additional
+	// FDs present at the start of the test (for example, opened by libc), those
+	// may be closed due to a timeout of some sort. Allow those to go away, but
+	// check that no new FDs are added.
+	for _, fd := range openFDs() {
+		if !old[fd] {
+			t.Errorf("leaked file descriptor %v", fd)
+		}
+	}
+}
+
+func TestExtraFiles(t *testing.T) {
+	if testing.Short() {
+		t.Skipf("skipping test in short mode that would build a helper binary")
+	}
+
+	if haveUnexpectedFDs {
+		// The point of this test is to make sure that any
+		// descriptors we open are marked close-on-exec.
+		// If haveUnexpectedFDs is true then there were other
+		// descriptors open when we started the test,
+		// so those descriptors are clearly not close-on-exec,
+		// and they will confuse the test. We could modify
+		// the test to expect those descriptors to remain open,
+		// but since we don't know where they came from or what
+		// they are doing, that seems fragile. For example,
+		// perhaps they are from the startup code on this
+		// system for some reason. Also, this test is not
+		// system-specific; as long as most systems do not skip
+		// the test, we will still be testing what we care about.
+		t.Skip("skipping test because test was run with FDs open")
+	}
+
+	testenv.MustHaveExec(t)
+	testenv.MustHaveGoBuild(t)
+
+	// This test runs with cgo disabled. External linking needs cgo, so
+	// it doesn't work if external linking is required.
+	testenv.MustInternalLink(t, false)
+
+	if runtime.GOOS == "windows" {
+		t.Skipf("skipping test on %q", runtime.GOOS)
+	}
+
+	// Force network usage, to verify the epoll (or whatever) fd
+	// doesn't leak to the child,
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	// Make sure duplicated fds don't leak to the child.
+	f, err := ln.(*net.TCPListener).File()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	ln2, err := net.FileListener(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln2.Close()
+
+	// Force TLS root certs to be loaded (which might involve
+	// cgo), to make sure none of that potential C code leaks fds.
+	ts := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	// quiet expected TLS handshake error "remote error: bad certificate"
+	ts.Config.ErrorLog = log.New(io.Discard, "", 0)
+	ts.StartTLS()
+	defer ts.Close()
+	_, err = http.Get(ts.URL)
+	if err == nil {
+		t.Errorf("success trying to fetch %s; want an error", ts.URL)
+	}
+
+	tf, err := os.CreateTemp("", "")
+	if err != nil {
+		t.Fatalf("TempFile: %v", err)
+	}
+	defer os.Remove(tf.Name())
+	defer tf.Close()
+
+	const text = "Hello, fd 3!"
+	_, err = tf.Write([]byte(text))
+	if err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+	_, err = tf.Seek(0, io.SeekStart)
+	if err != nil {
+		t.Fatalf("Seek: %v", err)
+	}
+
+	tempdir := t.TempDir()
+	exe := filepath.Join(tempdir, "read3.exe")
+
+	c := testenv.Command(t, testenv.GoToolPath(t), "build", "-o", exe, "read3.go")
+	// Build the test without cgo, so that C library functions don't
+	// open descriptors unexpectedly. See issue 25628.
+	c.Env = append(os.Environ(), "CGO_ENABLED=0")
+	if output, err := c.CombinedOutput(); err != nil {
+		t.Logf("go build -o %s read3.go\n%s", exe, output)
+		t.Fatalf("go build failed: %v", err)
+	}
+
+	// Use a deadline to try to get some output even if the program hangs.
+	ctx := context.Background()
+	if deadline, ok := t.Deadline(); ok {
+		// Leave a 20% grace period to flush output, which may be large on the
+		// linux/386 builders because we're running the subprocess under strace.
+		deadline = deadline.Add(-time.Until(deadline) / 5)
+
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithDeadline(ctx, deadline)
+		defer cancel()
+	}
+
+	c = exec.CommandContext(ctx, exe)
+	var stdout, stderr strings.Builder
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+	c.ExtraFiles = []*os.File{tf}
+	if runtime.GOOS == "illumos" {
+		// Some facilities in illumos are implemented via access
+		// to /proc by libc; such accesses can briefly occupy a
+		// low-numbered fd.  If this occurs concurrently with the
+		// test that checks for leaked descriptors, the check can
+		// become confused and report a spurious leaked descriptor.
+		// (See issue #42431 for more detailed analysis.)
+		//
+		// Attempt to constrain the use of additional threads in the
+		// child process to make this test less flaky:
+		c.Env = append(os.Environ(), "GOMAXPROCS=1")
+	}
+	err = c.Run()
+	if err != nil {
+		t.Fatalf("Run: %v\n--- stdout:\n%s--- stderr:\n%s", err, stdout.String(), stderr.String())
+	}
+	if stdout.String() != text {
+		t.Errorf("got stdout %q, stderr %q; want %q on stdout", stdout.String(), stderr.String(), text)
+	}
+}
+
+func TestExtraFilesRace(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		maySkipHelperCommand("describefiles")
+		t.Skip("no operating system support; skipping")
+	}
+	t.Parallel()
+
+	listen := func() net.Listener {
+		ln, err := net.Listen("tcp", "127.0.0.1:0")
+		if err != nil {
+			t.Fatal(err)
+		}
+		return ln
+	}
+	listenerFile := func(ln net.Listener) *os.File {
+		f, err := ln.(*net.TCPListener).File()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return f
+	}
+	runCommand := func(c *exec.Cmd, out chan<- string) {
+		bout, err := c.CombinedOutput()
+		if err != nil {
+			out <- "ERROR:" + err.Error()
+		} else {
+			out <- string(bout)
+		}
+	}
+
+	for i := 0; i < 10; i++ {
+		if testing.Short() && i >= 3 {
+			break
+		}
+		la := listen()
+		ca := helperCommand(t, "describefiles")
+		ca.ExtraFiles = []*os.File{listenerFile(la)}
+		lb := listen()
+		cb := helperCommand(t, "describefiles")
+		cb.ExtraFiles = []*os.File{listenerFile(lb)}
+		ares := make(chan string)
+		bres := make(chan string)
+		go runCommand(ca, ares)
+		go runCommand(cb, bres)
+		if got, want := <-ares, fmt.Sprintf("fd3: listener %s\n", la.Addr()); got != want {
+			t.Errorf("iteration %d, process A got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		if got, want := <-bres, fmt.Sprintf("fd3: listener %s\n", lb.Addr()); got != want {
+			t.Errorf("iteration %d, process B got:\n%s\nwant:\n%s\n", i, got, want)
+		}
+		la.Close()
+		lb.Close()
+		for _, f := range ca.ExtraFiles {
+			f.Close()
+		}
+		for _, f := range cb.ExtraFiles {
+			f.Close()
+		}
+	}
+}
+
+type delayedInfiniteReader struct{}
+
+func (delayedInfiniteReader) Read(b []byte) (int, error) {
+	time.Sleep(100 * time.Millisecond)
+	for i := range b {
+		b[i] = 'x'
+	}
+	return len(b), nil
+}
+
+// Issue 9173: ignore stdin pipe writes if the program completes successfully.
+func TestIgnorePipeErrorOnSuccess(t *testing.T) {
+	t.Parallel()
+
+	testWith := func(r io.Reader) func(*testing.T) {
+		return func(t *testing.T) {
+			t.Parallel()
+
+			cmd := helperCommand(t, "echo", "foo")
+			var out strings.Builder
+			cmd.Stdin = r
+			cmd.Stdout = &out
+			if err := cmd.Run(); err != nil {
+				t.Fatal(err)
+			}
+			if got, want := out.String(), "foo\n"; got != want {
+				t.Errorf("output = %q; want %q", got, want)
+			}
+		}
+	}
+	t.Run("10MB", testWith(strings.NewReader(strings.Repeat("x", 10<<20))))
+	t.Run("Infinite", testWith(delayedInfiniteReader{}))
+}
+
+type badWriter struct{}
+
+func (w *badWriter) Write(data []byte) (int, error) {
+	return 0, io.ErrUnexpectedEOF
+}
+
+func TestClosePipeOnCopyError(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "yes")
+	cmd.Stdout = new(badWriter)
+	err := cmd.Run()
+	if err == nil {
+		t.Errorf("yes unexpectedly completed successfully")
+	}
+}
+
+func TestOutputStderrCapture(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "stderrfail")
+	_, err := cmd.Output()
+	ee, ok := err.(*exec.ExitError)
+	if !ok {
+		t.Fatalf("Output error type = %T; want ExitError", err)
+	}
+	got := string(ee.Stderr)
+	want := "some stderr text\n"
+	if got != want {
+		t.Errorf("ExitError.Stderr = %q; want %q", got, want)
+	}
+}
+
+func TestContext(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	c := helperCommandContext(t, ctx, "pipetest")
+	stdin, err := c.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stdout, err := c.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := c.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := stdin.Write([]byte("O:hi\n")); err != nil {
+		t.Fatal(err)
+	}
+	buf := make([]byte, 5)
+	n, err := io.ReadFull(stdout, buf)
+	if n != len(buf) || err != nil || string(buf) != "O:hi\n" {
+		t.Fatalf("ReadFull = %d, %v, %q", n, err, buf[:n])
+	}
+	go cancel()
+
+	if err := c.Wait(); err == nil {
+		t.Fatal("expected Wait failure")
+	}
+}
+
+func TestContextCancel(t *testing.T) {
+	if runtime.GOOS == "netbsd" && runtime.GOARCH == "arm64" {
+		maySkipHelperCommand("cat")
+		testenv.SkipFlaky(t, 42061)
+	}
+
+	// To reduce noise in the final goroutine dump,
+	// let other parallel tests complete if possible.
+	t.Parallel()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	c := helperCommandContext(t, ctx, "cat")
+
+	stdin, err := c.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer stdin.Close()
+
+	if err := c.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	// At this point the process is alive. Ensure it by sending data to stdin.
+	if _, err := io.WriteString(stdin, "echo"); err != nil {
+		t.Fatal(err)
+	}
+
+	cancel()
+
+	// Calling cancel should have killed the process, so writes
+	// should now fail.  Give the process a little while to die.
+	start := time.Now()
+	delay := 1 * time.Millisecond
+	for {
+		if _, err := io.WriteString(stdin, "echo"); err != nil {
+			break
+		}
+
+		if time.Since(start) > time.Minute {
+			// Panic instead of calling t.Fatal so that we get a goroutine dump.
+			// We want to know exactly what the os/exec goroutines got stuck on.
+			debug.SetTraceback("system")
+			panic("canceling context did not stop program")
+		}
+
+		// Back off exponentially (up to 1-second sleeps) to give the OS time to
+		// terminate the process.
+		delay *= 2
+		if delay > 1*time.Second {
+			delay = 1 * time.Second
+		}
+		time.Sleep(delay)
+	}
+
+	if err := c.Wait(); err == nil {
+		t.Error("program unexpectedly exited successfully")
+	} else {
+		t.Logf("exit status: %v", err)
+	}
+}
+
+// test that environment variables are de-duped.
+func TestDedupEnvEcho(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "echoenv", "FOO")
+	cmd.Env = append(cmd.Environ(), "FOO=bad", "FOO=good")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := strings.TrimSpace(string(out)), "good"; got != want {
+		t.Errorf("output = %q; want %q", got, want)
+	}
+}
+
+func TestEnvNULCharacter(t *testing.T) {
+	if runtime.GOOS == "plan9" {
+		t.Skip("plan9 explicitly allows NUL in the environment")
+	}
+	cmd := helperCommand(t, "echoenv", "FOO", "BAR")
+	cmd.Env = append(cmd.Environ(), "FOO=foo\x00BAR=bar")
+	out, err := cmd.CombinedOutput()
+	if err == nil {
+		t.Errorf("output = %q; want error", string(out))
+	}
+}
+
+func TestString(t *testing.T) {
+	t.Parallel()
+
+	echoPath, err := exec.LookPath("echo")
+	if err != nil {
+		t.Skip(err)
+	}
+	tests := [...]struct {
+		path string
+		args []string
+		want string
+	}{
+		{"echo", nil, echoPath},
+		{"echo", []string{"a"}, echoPath + " a"},
+		{"echo", []string{"a", "b"}, echoPath + " a b"},
+	}
+	for _, test := range tests {
+		cmd := exec.Command(test.path, test.args...)
+		if got := cmd.String(); got != test.want {
+			t.Errorf("String(%q, %q) = %q, want %q", test.path, test.args, got, test.want)
+		}
+	}
+}
+
+func TestStringPathNotResolved(t *testing.T) {
+	t.Parallel()
+
+	_, err := exec.LookPath("makemeasandwich")
+	if err == nil {
+		t.Skip("wow, thanks")
+	}
+
+	cmd := exec.Command("makemeasandwich", "-lettuce")
+	want := "makemeasandwich -lettuce"
+	if got := cmd.String(); got != want {
+		t.Errorf("String(%q, %q) = %q, want %q", "makemeasandwich", "-lettuce", got, want)
+	}
+}
+
+func TestNoPath(t *testing.T) {
+	err := new(exec.Cmd).Start()
+	want := "exec: no command"
+	if err == nil || err.Error() != want {
+		t.Errorf("new(Cmd).Start() = %v, want %q", err, want)
+	}
+}
+
+// TestDoubleStartLeavesPipesOpen checks for a regression in which calling
+// Start twice, which returns an error on the second call, would spuriously
+// close the pipes established in the first call.
+func TestDoubleStartLeavesPipesOpen(t *testing.T) {
+	t.Parallel()
+
+	cmd := helperCommand(t, "pipetest")
+	in, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	out, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := cmd.Wait(); err != nil {
+			t.Error(err)
+		}
+	})
+
+	if err := cmd.Start(); err == nil || !strings.HasSuffix(err.Error(), "already started") {
+		t.Fatalf("second call to Start returned a nil; want an 'already started' error")
+	}
+
+	outc := make(chan []byte, 1)
+	go func() {
+		b, err := io.ReadAll(out)
+		if err != nil {
+			t.Error(err)
+		}
+		outc <- b
+	}()
+
+	const msg = "O:Hello, pipe!\n"
+
+	_, err = io.WriteString(in, msg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	in.Close()
+
+	b := <-outc
+	if !bytes.Equal(b, []byte(msg)) {
+		t.Fatalf("read %q from stdout pipe; want %q", b, msg)
+	}
+}
+
+func cmdHang(args ...string) {
+	sleep, err := time.ParseDuration(args[0])
+	if err != nil {
+		panic(err)
+	}
+
+	fs := flag.NewFlagSet("hang", flag.ExitOnError)
+	exitOnInterrupt := fs.Bool("interrupt", false, "if true, commands should exit 0 on os.Interrupt")
+	subsleep := fs.Duration("subsleep", 0, "amount of time for the 'hang' helper to leave an orphaned subprocess sleeping with stderr open")
+	probe := fs.Duration("probe", 0, "if nonzero, the 'hang' helper should write to stderr at this interval, and exit nonzero if a write fails")
+	read := fs.Bool("read", false, "if true, the 'hang' helper should read stdin to completion before sleeping")
+	fs.Parse(args[1:])
+
+	pid := os.Getpid()
+
+	if *subsleep != 0 {
+		cmd := exec.Command(exePath(nil), "hang", subsleep.String(), "-read=true", "-probe="+probe.String())
+		cmd.Stdin = os.Stdin
+		cmd.Stderr = os.Stderr
+		out, err := cmd.StdoutPipe()
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		cmd.Start()
+
+		buf := new(strings.Builder)
+		if _, err := io.Copy(buf, out); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			cmd.Process.Kill()
+			cmd.Wait()
+			os.Exit(1)
+		}
+		fmt.Fprintf(os.Stderr, "%d: started %d: %v\n", pid, cmd.Process.Pid, cmd)
+		go cmd.Wait() // Release resources if cmd happens not to outlive this process.
+	}
+
+	if *exitOnInterrupt {
+		c := make(chan os.Signal, 1)
+		signal.Notify(c, os.Interrupt)
+		go func() {
+			sig := <-c
+			fmt.Fprintf(os.Stderr, "%d: received %v\n", pid, sig)
+			os.Exit(0)
+		}()
+	} else {
+		signal.Ignore(os.Interrupt)
+	}
+
+	// Signal that the process is set up by closing stdout.
+	os.Stdout.Close()
+
+	if *read {
+		if pipeSignal != nil {
+			signal.Ignore(pipeSignal)
+		}
+		r := bufio.NewReader(os.Stdin)
+		for {
+			line, err := r.ReadBytes('\n')
+			if len(line) > 0 {
+				// Ignore write errors: we want to keep reading even if stderr is closed.
+				fmt.Fprintf(os.Stderr, "%d: read %s", pid, line)
+			}
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "%d: finished read: %v", pid, err)
+				break
+			}
+		}
+	}
+
+	if *probe != 0 {
+		ticker := time.NewTicker(*probe)
+		go func() {
+			for range ticker.C {
+				if _, err := fmt.Fprintf(os.Stderr, "%d: ok\n", pid); err != nil {
+					os.Exit(1)
+				}
+			}
+		}()
+	}
+
+	if sleep != 0 {
+		time.Sleep(sleep)
+		fmt.Fprintf(os.Stderr, "%d: slept %v\n", pid, sleep)
+	}
+}
+
+// A tickReader reads an unbounded sequence of timestamps at no more than a
+// fixed interval.
+type tickReader struct {
+	interval time.Duration
+	lastTick time.Time
+	s        string
+}
+
+func newTickReader(interval time.Duration) *tickReader {
+	return &tickReader{interval: interval}
+}
+
+func (r *tickReader) Read(p []byte) (n int, err error) {
+	if len(r.s) == 0 {
+		if d := r.interval - time.Since(r.lastTick); d > 0 {
+			time.Sleep(d)
+		}
+		r.lastTick = time.Now()
+		r.s = r.lastTick.Format(time.RFC3339Nano + "\n")
+	}
+
+	n = copy(p, r.s)
+	r.s = r.s[n:]
+	return n, nil
+}
+
+func startHang(t *testing.T, ctx context.Context, hangTime time.Duration, interrupt os.Signal, waitDelay time.Duration, flags ...string) *exec.Cmd {
+	t.Helper()
+
+	args := append([]string{hangTime.String()}, flags...)
+	cmd := helperCommandContext(t, ctx, "hang", args...)
+	cmd.Stdin = newTickReader(1 * time.Millisecond)
+	cmd.Stderr = new(strings.Builder)
+	if interrupt == nil {
+		cmd.Cancel = nil
+	} else {
+		cmd.Cancel = func() error {
+			return cmd.Process.Signal(interrupt)
+		}
+	}
+	cmd.WaitDelay = waitDelay
+	out, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Log(cmd)
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Wait for cmd to close stdout to signal that its handlers are installed.
+	buf := new(strings.Builder)
+	if _, err := io.Copy(buf, out); err != nil {
+		t.Error(err)
+		cmd.Process.Kill()
+		cmd.Wait()
+		t.FailNow()
+	}
+	if buf.Len() > 0 {
+		t.Logf("stdout %v:\n%s", cmd.Args, buf)
+	}
+
+	return cmd
+}
+
+func TestWaitInterrupt(t *testing.T) {
+	t.Parallel()
+
+	// tooLong is an arbitrary duration that is expected to be much longer than
+	// the test runs, but short enough that leaked processes will eventually exit
+	// on their own.
+	const tooLong = 10 * time.Minute
+
+	// Control case: with no cancellation and no WaitDelay, we should wait for the
+	// process to exit.
+	t.Run("Wait", func(t *testing.T) {
+		t.Parallel()
+		cmd := startHang(t, context.Background(), 1*time.Millisecond, os.Kill, 0)
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		if err != nil {
+			t.Errorf("Wait: %v; want <nil>", err)
+		}
+		if ps := cmd.ProcessState; !ps.Exited() {
+			t.Errorf("cmd did not exit: %v", ps)
+		} else if code := ps.ExitCode(); code != 0 {
+			t.Errorf("cmd.ProcessState.ExitCode() = %v; want 0", code)
+		}
+	})
+
+	// With a very long WaitDelay and no Cancel function, we should wait for the
+	// process to exit even if the command's Context is cancelled.
+	t.Run("WaitDelay", func(t *testing.T) {
+		if runtime.GOOS == "windows" {
+			t.Skipf("skipping: os.Interrupt is not implemented on Windows")
+		}
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := startHang(t, ctx, tooLong, nil, tooLong, "-interrupt=true")
+		cancel()
+
+		time.Sleep(1 * time.Millisecond)
+		// At this point cmd should still be running (because we passed nil to
+		// startHang for the cancel signal). Sending it an explicit Interrupt signal
+		// should succeed.
+		if err := cmd.Process.Signal(os.Interrupt); err != nil {
+			t.Error(err)
+		}
+
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// This program exits with status 0,
+		// but pretty much always does so during the wait delay.
+		// Since the Cmd itself didn't do anything to stop the process when the
+		// context expired, a successful exit is valid (even if late) and does
+		// not merit a non-nil error.
+		if err != nil {
+			t.Errorf("Wait: %v; want nil", err)
+		}
+		if ps := cmd.ProcessState; !ps.Exited() {
+			t.Errorf("cmd did not exit: %v", ps)
+		} else if code := ps.ExitCode(); code != 0 {
+			t.Errorf("cmd.ProcessState.ExitCode() = %v; want 0", code)
+		}
+	})
+
+	// If the context is cancelled and the Cancel function sends os.Kill,
+	// the process should be terminated immediately, and its output
+	// pipes should be closed (causing Wait to return) after WaitDelay
+	// even if a child process is still writing to them.
+	t.Run("SIGKILL-hang", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := startHang(t, ctx, tooLong, os.Kill, 10*time.Millisecond, "-subsleep=10m", "-probe=1ms")
+		cancel()
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// This test should kill the child process after 10ms,
+		// leaving a grandchild process writing probes in a loop.
+		// The child process should be reported as failed,
+		// and the grandchild will exit (or die by SIGPIPE) once the
+		// stderr pipe is closed.
+		if ee := new(*exec.ExitError); !errors.As(err, ee) {
+			t.Errorf("Wait error = %v; want %T", err, *ee)
+		}
+	})
+
+	// If the process exits with status 0 but leaves a child behind writing
+	// to its output pipes, Wait should only wait for WaitDelay before
+	// closing the pipes and returning.  Wait should return ErrWaitDelay
+	// to indicate that the piped output may be incomplete even though the
+	// command returned a “success” code.
+	t.Run("Exit-hang", func(t *testing.T) {
+		t.Parallel()
+
+		cmd := startHang(t, context.Background(), 1*time.Millisecond, nil, 10*time.Millisecond, "-subsleep=10m", "-probe=1ms")
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// This child process should exit immediately,
+		// leaving a grandchild process writing probes in a loop.
+		// Since the child has no ExitError to report but we did not
+		// read all of its output, Wait should return ErrWaitDelay.
+		if !errors.Is(err, exec.ErrWaitDelay) {
+			t.Errorf("Wait error = %v; want %T", err, exec.ErrWaitDelay)
+		}
+	})
+
+	// If the Cancel function sends a signal that the process can handle, and it
+	// handles that signal without actually exiting, then it should be terminated
+	// after the WaitDelay.
+	t.Run("SIGINT-ignored", func(t *testing.T) {
+		if runtime.GOOS == "windows" {
+			t.Skipf("skipping: os.Interrupt is not implemented on Windows")
+		}
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := startHang(t, ctx, tooLong, os.Interrupt, 10*time.Millisecond, "-interrupt=false")
+		cancel()
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// This command ignores SIGINT, sleeping until it is killed.
+		// Wait should return the usual error for a killed process.
+		if ee := new(*exec.ExitError); !errors.As(err, ee) {
+			t.Errorf("Wait error = %v; want %T", err, *ee)
+		}
+	})
+
+	// If the process handles the cancellation signal and exits with status 0,
+	// Wait should report a non-nil error (because the process had to be
+	// interrupted), and it should be a context error (because there is no error
+	// to report from the child process itself).
+	t.Run("SIGINT-handled", func(t *testing.T) {
+		if runtime.GOOS == "windows" {
+			t.Skipf("skipping: os.Interrupt is not implemented on Windows")
+		}
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := startHang(t, ctx, tooLong, os.Interrupt, 0, "-interrupt=true")
+		cancel()
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		if !errors.Is(err, ctx.Err()) {
+			t.Errorf("Wait error = %v; want %v", err, ctx.Err())
+		}
+		if ps := cmd.ProcessState; !ps.Exited() {
+			t.Errorf("cmd did not exit: %v", ps)
+		} else if code := ps.ExitCode(); code != 0 {
+			t.Errorf("cmd.ProcessState.ExitCode() = %v; want 0", code)
+		}
+	})
+
+	// If the Cancel function sends SIGQUIT, it should be handled in the usual
+	// way: a Go program should dump its goroutines and exit with non-success
+	// status. (We expect SIGQUIT to be a common pattern in real-world use.)
+	t.Run("SIGQUIT", func(t *testing.T) {
+		if quitSignal == nil {
+			t.Skipf("skipping: SIGQUIT is not supported on %v", runtime.GOOS)
+		}
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := startHang(t, ctx, tooLong, quitSignal, 0)
+		cancel()
+		err := cmd.Wait()
+		t.Logf("stderr:\n%s", cmd.Stderr)
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		if ee := new(*exec.ExitError); !errors.As(err, ee) {
+			t.Errorf("Wait error = %v; want %v", err, ctx.Err())
+		}
+
+		if ps := cmd.ProcessState; !ps.Exited() {
+			t.Errorf("cmd did not exit: %v", ps)
+		} else if code := ps.ExitCode(); code != 2 {
+			// The default os/signal handler exits with code 2.
+			t.Errorf("cmd.ProcessState.ExitCode() = %v; want 2", code)
+		}
+
+		if !strings.Contains(fmt.Sprint(cmd.Stderr), "\n\ngoroutine ") {
+			t.Errorf("cmd.Stderr does not contain a goroutine dump")
+		}
+	})
+}
+
+func TestCancelErrors(t *testing.T) {
+	t.Parallel()
+
+	// If Cancel returns a non-ErrProcessDone error and the process
+	// exits successfully, Wait should wrap the error from Cancel.
+	t.Run("success after error", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		cmd := helperCommandContext(t, ctx, "pipetest")
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		errArbitrary := errors.New("arbitrary error")
+		cmd.Cancel = func() error {
+			stdin.Close()
+			t.Logf("Cancel returning %v", errArbitrary)
+			return errArbitrary
+		}
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		cancel()
+
+		err = cmd.Wait()
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+		if !errors.Is(err, errArbitrary) || err == errArbitrary {
+			t.Errorf("Wait error = %v; want an error wrapping %v", err, errArbitrary)
+		}
+	})
+
+	// If Cancel returns an error equivalent to ErrProcessDone,
+	// Wait should ignore that error. (ErrProcessDone indicates that the
+	// process was already done before we tried to interrupt it — maybe we
+	// just didn't notice because Wait hadn't been called yet.)
+	t.Run("success after ErrProcessDone", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		cmd := helperCommandContext(t, ctx, "pipetest")
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		stdout, err := cmd.StdoutPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// We intentionally race Cancel against the process exiting,
+		// but ensure that the process wins the race (and return ErrProcessDone
+		// from Cancel to report that).
+		interruptCalled := make(chan struct{})
+		done := make(chan struct{})
+		cmd.Cancel = func() error {
+			close(interruptCalled)
+			<-done
+			t.Logf("Cancel returning an error wrapping ErrProcessDone")
+			return fmt.Errorf("%w: stdout closed", os.ErrProcessDone)
+		}
+
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+
+		cancel()
+		<-interruptCalled
+		stdin.Close()
+		io.Copy(io.Discard, stdout) // reaches EOF when the process exits
+		close(done)
+
+		err = cmd.Wait()
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+		if err != nil {
+			t.Errorf("Wait error = %v; want nil", err)
+		}
+	})
+
+	// If Cancel returns an error and the process is killed after
+	// WaitDelay, Wait should report the usual SIGKILL ExitError, not the
+	// error from Cancel.
+	t.Run("killed after error", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		cmd := helperCommandContext(t, ctx, "pipetest")
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer stdin.Close()
+
+		errArbitrary := errors.New("arbitrary error")
+		var interruptCalled atomic.Bool
+		cmd.Cancel = func() error {
+			t.Logf("Cancel called")
+			interruptCalled.Store(true)
+			return errArbitrary
+		}
+		cmd.WaitDelay = 1 * time.Millisecond
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		cancel()
+
+		err = cmd.Wait()
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// Ensure that Cancel actually had the opportunity to
+		// return the error.
+		if !interruptCalled.Load() {
+			t.Errorf("Cancel was not called when the context was canceled")
+		}
+
+		// This test should kill the child process after 1ms,
+		// To maximize compatibility with existing uses of exec.CommandContext, the
+		// resulting error should be an exec.ExitError without additional wrapping.
+		if ee, ok := err.(*exec.ExitError); !ok {
+			t.Errorf("Wait error = %v; want %T", err, *ee)
+		}
+	})
+
+	// If Cancel returns ErrProcessDone but the process is not actually done
+	// (and has to be killed), Wait should report the usual SIGKILL ExitError,
+	// not the error from Cancel.
+	t.Run("killed after spurious ErrProcessDone", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		cmd := helperCommandContext(t, ctx, "pipetest")
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer stdin.Close()
+
+		var interruptCalled atomic.Bool
+		cmd.Cancel = func() error {
+			t.Logf("Cancel returning an error wrapping ErrProcessDone")
+			interruptCalled.Store(true)
+			return fmt.Errorf("%w: stdout closed", os.ErrProcessDone)
+		}
+		cmd.WaitDelay = 1 * time.Millisecond
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		cancel()
+
+		err = cmd.Wait()
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		// Ensure that Cancel actually had the opportunity to
+		// return the error.
+		if !interruptCalled.Load() {
+			t.Errorf("Cancel was not called when the context was canceled")
+		}
+
+		// This test should kill the child process after 1ms,
+		// To maximize compatibility with existing uses of exec.CommandContext, the
+		// resulting error should be an exec.ExitError without additional wrapping.
+		if ee, ok := err.(*exec.ExitError); !ok {
+			t.Errorf("Wait error of type %T; want %T", err, ee)
+		}
+	})
+
+	// If Cancel returns an error and the process exits with an
+	// unsuccessful exit code, the process error should take precedence over the
+	// Cancel error.
+	t.Run("nonzero exit after error", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		cmd := helperCommandContext(t, ctx, "stderrfail")
+		stderr, err := cmd.StderrPipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		errArbitrary := errors.New("arbitrary error")
+		interrupted := make(chan struct{})
+		cmd.Cancel = func() error {
+			close(interrupted)
+			return errArbitrary
+		}
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		cancel()
+		<-interrupted
+		io.Copy(io.Discard, stderr)
+
+		err = cmd.Wait()
+		t.Logf("[%d] %v", cmd.Process.Pid, err)
+
+		if ee, ok := err.(*exec.ExitError); !ok || ee.ProcessState.ExitCode() != 1 {
+			t.Errorf("Wait error = %v; want exit status 1", err)
+		}
+	})
+}
+
+// TestConcurrentExec is a regression test for https://go.dev/issue/61080.
+//
+// Forking multiple child processes concurrently would sometimes hang on darwin.
+// (This test hung on a gomote with -count=100 after only a few iterations.)
+func TestConcurrentExec(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// This test will spawn nHangs subprocesses that hang reading from stdin,
+	// and nExits subprocesses that exit immediately.
+	//
+	// When issue #61080 was present, a long-lived "hang" subprocess would
+	// occasionally inherit the fork/exec status pipe from an "exit" subprocess,
+	// causing the parent process (which expects to see an EOF on that pipe almost
+	// immediately) to unexpectedly block on reading from the pipe.
+	var (
+		nHangs       = runtime.GOMAXPROCS(0)
+		nExits       = runtime.GOMAXPROCS(0)
+		hangs, exits sync.WaitGroup
+	)
+	hangs.Add(nHangs)
+	exits.Add(nExits)
+
+	// ready is done when the goroutines have done as much work as possible to
+	// prepare to create subprocesses. It isn't strictly necessary for the test,
+	// but helps to increase the repro rate by making it more likely that calls to
+	// syscall.StartProcess for the "hang" and "exit" goroutines overlap.
+	var ready sync.WaitGroup
+	ready.Add(nHangs + nExits)
+
+	for i := 0; i < nHangs; i++ {
+		go func() {
+			defer hangs.Done()
+
+			cmd := helperCommandContext(t, ctx, "pipetest")
+			stdin, err := cmd.StdinPipe()
+			if err != nil {
+				ready.Done()
+				t.Error(err)
+				return
+			}
+			cmd.Cancel = stdin.Close
+			ready.Done()
+
+			ready.Wait()
+			if err := cmd.Start(); err != nil {
+				if !errors.Is(err, context.Canceled) {
+					t.Error(err)
+				}
+				return
+			}
+
+			cmd.Wait()
+		}()
+	}
+
+	for i := 0; i < nExits; i++ {
+		go func() {
+			defer exits.Done()
+
+			cmd := helperCommandContext(t, ctx, "exit", "0")
+			ready.Done()
+
+			ready.Wait()
+			if err := cmd.Run(); err != nil {
+				t.Error(err)
+			}
+		}()
+	}
+
+	exits.Wait()
+	cancel()
+	hangs.Wait()
+}
+
+// TestPathRace tests that [Cmd.String] can be called concurrently
+// with [Cmd.Start].
+func TestPathRace(t *testing.T) {
+	cmd := helperCommand(t, "exit", "0")
+
+	done := make(chan struct{})
+	go func() {
+		out, err := cmd.CombinedOutput()
+		t.Logf("%v: %v\n%s", cmd, err, out)
+		close(done)
+	}()
+
+	t.Logf("running in background: %v", cmd)
+	<-done
+}
diff --git a/src/os/exec/exec_unix.go b/src/os/exec/exec_unix.go
new file mode 100644
index 0000000..3ed672a
--- /dev/null
+++ b/src/os/exec/exec_unix.go
@@ -0,0 +1,24 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !plan9 && !windows
+
+package exec
+
+import (
+	"io/fs"
+	"syscall"
+)
+
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore EPIPE errors copying to stdin if the program
+	// completed successfully otherwise.
+	// See Issue 9173.
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		pe.Err == syscall.EPIPE
+}
diff --git a/src/os/exec/exec_unix_test.go b/src/os/exec/exec_unix_test.go
new file mode 100644
index 0000000..d26c93a
--- /dev/null
+++ b/src/os/exec/exec_unix_test.go
@@ -0,0 +1,17 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package exec_test
+
+import (
+	"os"
+	"syscall"
+)
+
+var (
+	quitSignal os.Signal = syscall.SIGQUIT
+	pipeSignal os.Signal = syscall.SIGPIPE
+)
diff --git a/src/os/exec/exec_windows.go b/src/os/exec/exec_windows.go
new file mode 100644
index 0000000..e7a2ee6
--- /dev/null
+++ b/src/os/exec/exec_windows.go
@@ -0,0 +1,23 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"io/fs"
+	"syscall"
+)
+
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+func skipStdinCopyError(err error) bool {
+	// Ignore ERROR_BROKEN_PIPE and ERROR_NO_DATA errors copying
+	// to stdin if the program completed successfully otherwise.
+	// See Issue 20445.
+	const _ERROR_NO_DATA = syscall.Errno(0xe8)
+	pe, ok := err.(*fs.PathError)
+	return ok &&
+		pe.Op == "write" && pe.Path == "|1" &&
+		(pe.Err == syscall.ERROR_BROKEN_PIPE || pe.Err == _ERROR_NO_DATA)
+}
diff --git a/src/os/exec/exec_windows_test.go b/src/os/exec/exec_windows_test.go
new file mode 100644
index 0000000..efd3710
--- /dev/null
+++ b/src/os/exec/exec_windows_test.go
@@ -0,0 +1,109 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build windows
+
+package exec_test
+
+import (
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"syscall"
+	"testing"
+)
+
+var (
+	quitSignal os.Signal = nil
+	pipeSignal os.Signal = syscall.SIGPIPE
+)
+
+func init() {
+	registerHelperCommand("pipehandle", cmdPipeHandle)
+}
+
+func cmdPipeHandle(args ...string) {
+	handle, _ := strconv.ParseUint(args[0], 16, 64)
+	pipe := os.NewFile(uintptr(handle), "")
+	_, err := fmt.Fprint(pipe, args[1])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "writing to pipe failed: %v\n", err)
+		os.Exit(1)
+	}
+	pipe.Close()
+}
+
+func TestPipePassing(t *testing.T) {
+	t.Parallel()
+
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Error(err)
+	}
+	const marker = "arrakis, dune, desert planet"
+	childProc := helperCommand(t, "pipehandle", strconv.FormatUint(uint64(w.Fd()), 16), marker)
+	childProc.SysProcAttr = &syscall.SysProcAttr{AdditionalInheritedHandles: []syscall.Handle{syscall.Handle(w.Fd())}}
+	err = childProc.Start()
+	if err != nil {
+		t.Error(err)
+	}
+	w.Close()
+	response, err := io.ReadAll(r)
+	if err != nil {
+		t.Error(err)
+	}
+	r.Close()
+	if string(response) != marker {
+		t.Errorf("got %q; want %q", string(response), marker)
+	}
+	err = childProc.Wait()
+	if err != nil {
+		t.Error(err)
+	}
+}
+
+func TestNoInheritHandles(t *testing.T) {
+	t.Parallel()
+
+	cmd := testenv.Command(t, "cmd", "/c exit 88")
+	cmd.SysProcAttr = &syscall.SysProcAttr{NoInheritHandles: true}
+	err := cmd.Run()
+	exitError, ok := err.(*exec.ExitError)
+	if !ok {
+		t.Fatalf("got error %v; want ExitError", err)
+	}
+	if exitError.ExitCode() != 88 {
+		t.Fatalf("got exit code %d; want 88", exitError.ExitCode())
+	}
+}
+
+// start a child process without the user code explicitly starting
+// with a copy of the parent's SYSTEMROOT.
+// (See issue 25210.)
+func TestChildCriticalEnv(t *testing.T) {
+	t.Parallel()
+	cmd := helperCommand(t, "echoenv", "SYSTEMROOT")
+
+	// Explicitly remove SYSTEMROOT from the command's environment.
+	var env []string
+	for _, kv := range cmd.Environ() {
+		k, _, ok := strings.Cut(kv, "=")
+		if !ok || !strings.EqualFold(k, "SYSTEMROOT") {
+			env = append(env, kv)
+		}
+	}
+	cmd.Env = env
+
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.TrimSpace(string(out)) == "" {
+		t.Error("no SYSTEMROOT found")
+	}
+}
diff --git a/src/os/exec/internal/fdtest/exists_plan9.go b/src/os/exec/internal/fdtest/exists_plan9.go
new file mode 100644
index 0000000..8886e06
--- /dev/null
+++ b/src/os/exec/internal/fdtest/exists_plan9.go
@@ -0,0 +1,20 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build plan9
+
+package fdtest
+
+import (
+	"syscall"
+)
+
+const errBadFd = syscall.ErrorString("fd out of range or not open")
+
+// Exists returns true if fd is a valid file descriptor.
+func Exists(fd uintptr) bool {
+	var buf [1]byte
+	_, err := syscall.Fstat(int(fd), buf[:])
+	return err != errBadFd
+}
diff --git a/src/os/exec/internal/fdtest/exists_test.go b/src/os/exec/internal/fdtest/exists_test.go
new file mode 100644
index 0000000..a02dddf
--- /dev/null
+++ b/src/os/exec/internal/fdtest/exists_test.go
@@ -0,0 +1,21 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fdtest
+
+import (
+	"os"
+	"runtime"
+	"testing"
+)
+
+func TestExists(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Exists not implemented for windows")
+	}
+
+	if !Exists(os.Stdout.Fd()) {
+		t.Errorf("Exists(%d) got false want true", os.Stdout.Fd())
+	}
+}
diff --git a/src/os/exec/internal/fdtest/exists_unix.go b/src/os/exec/internal/fdtest/exists_unix.go
new file mode 100644
index 0000000..472a802
--- /dev/null
+++ b/src/os/exec/internal/fdtest/exists_unix.go
@@ -0,0 +1,19 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix || wasm
+
+// Package fdtest provides test helpers for working with file descriptors across exec.
+package fdtest
+
+import (
+	"syscall"
+)
+
+// Exists returns true if fd is a valid file descriptor.
+func Exists(fd uintptr) bool {
+	var s syscall.Stat_t
+	err := syscall.Fstat(int(fd), &s)
+	return err != syscall.EBADF
+}
diff --git a/src/os/exec/internal/fdtest/exists_windows.go b/src/os/exec/internal/fdtest/exists_windows.go
new file mode 100644
index 0000000..72b8ccf
--- /dev/null
+++ b/src/os/exec/internal/fdtest/exists_windows.go
@@ -0,0 +1,12 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build windows
+
+package fdtest
+
+// Exists is not implemented on windows and panics.
+func Exists(fd uintptr) bool {
+	panic("unimplemented")
+}
diff --git a/src/os/exec/internal_test.go b/src/os/exec/internal_test.go
new file mode 100644
index 0000000..68d517f
--- /dev/null
+++ b/src/os/exec/internal_test.go
@@ -0,0 +1,61 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"io"
+	"testing"
+)
+
+func TestPrefixSuffixSaver(t *testing.T) {
+	tests := []struct {
+		N      int
+		writes []string
+		want   string
+	}{
+		{
+			N:      2,
+			writes: nil,
+			want:   "",
+		},
+		{
+			N:      2,
+			writes: []string{"a"},
+			want:   "a",
+		},
+		{
+			N:      2,
+			writes: []string{"abc", "d"},
+			want:   "abcd",
+		},
+		{
+			N:      2,
+			writes: []string{"abc", "d", "e"},
+			want:   "ab\n... omitting 1 bytes ...\nde",
+		},
+		{
+			N:      2,
+			writes: []string{"ab______________________yz"},
+			want:   "ab\n... omitting 22 bytes ...\nyz",
+		},
+		{
+			N:      2,
+			writes: []string{"ab_______________________y", "z"},
+			want:   "ab\n... omitting 23 bytes ...\nyz",
+		},
+	}
+	for i, tt := range tests {
+		w := &prefixSuffixSaver{N: tt.N}
+		for _, s := range tt.writes {
+			n, err := io.WriteString(w, s)
+			if err != nil || n != len(s) {
+				t.Errorf("%d. WriteString(%q) = %v, %v; want %v, %v", i, s, n, err, len(s), nil)
+			}
+		}
+		if got := string(w.Bytes()); got != tt.want {
+			t.Errorf("%d. Bytes = %q; want %q", i, got, tt.want)
+		}
+	}
+}
diff --git a/src/os/exec/lp_linux_test.go b/src/os/exec/lp_linux_test.go
new file mode 100644
index 0000000..a7f9aa2
--- /dev/null
+++ b/src/os/exec/lp_linux_test.go
@@ -0,0 +1,88 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec_test
+
+import (
+	"errors"
+	"internal/syscall/unix"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"syscall"
+	"testing"
+)
+
+func TestFindExecutableVsNoexec(t *testing.T) {
+	t.Parallel()
+
+	// This test case relies on faccessat2(2) syscall, which appeared in Linux v5.8.
+	if major, minor := unix.KernelVersion(); major < 5 || (major == 5 && minor < 8) {
+		t.Skip("requires Linux kernel v5.8 with faccessat2(2) syscall")
+	}
+
+	tmp := t.TempDir()
+
+	// Create a tmpfs mount.
+	err := syscall.Mount("tmpfs", tmp, "tmpfs", 0, "")
+	if testenv.SyscallIsNotSupported(err) {
+		// Usually this means lack of CAP_SYS_ADMIN, but there might be
+		// other reasons, especially in restricted test environments.
+		t.Skipf("requires ability to mount tmpfs (%v)", err)
+	} else if err != nil {
+		t.Fatalf("mount %s failed: %v", tmp, err)
+	}
+	t.Cleanup(func() {
+		if err := syscall.Unmount(tmp, 0); err != nil {
+			t.Error(err)
+		}
+	})
+
+	// Create an executable.
+	path := filepath.Join(tmp, "program")
+	err = os.WriteFile(path, []byte("#!/bin/sh\necho 123\n"), 0o755)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Check that it works as expected.
+	_, err = exec.LookPath(path)
+	if err != nil {
+		t.Fatalf("LookPath: got %v, want nil", err)
+	}
+
+	for {
+		err = exec.Command(path).Run()
+		if err == nil {
+			break
+		}
+		if errors.Is(err, syscall.ETXTBSY) {
+			// A fork+exec in another process may be holding open the FD that we used
+			// to write the executable (see https://go.dev/issue/22315).
+			// Since the descriptor should have CLOEXEC set, the problem should resolve
+			// as soon as the forked child reaches its exec call.
+			// Keep retrying until that happens.
+		} else {
+			t.Fatalf("exec: got %v, want nil", err)
+		}
+	}
+
+	// Remount with noexec flag.
+	err = syscall.Mount("", tmp, "", syscall.MS_REMOUNT|syscall.MS_NOEXEC, "")
+	if testenv.SyscallIsNotSupported(err) {
+		t.Skipf("requires ability to re-mount tmpfs (%v)", err)
+	} else if err != nil {
+		t.Fatalf("remount %s with noexec failed: %v", tmp, err)
+	}
+
+	if err := exec.Command(path).Run(); err == nil {
+		t.Fatal("exec on noexec filesystem: got nil, want error")
+	}
+
+	_, err = exec.LookPath(path)
+	if err == nil {
+		t.Fatalf("LookPath: got nil, want error")
+	}
+}
diff --git a/src/os/exec/lp_plan9.go b/src/os/exec/lp_plan9.go
new file mode 100644
index 0000000..dffdbac
--- /dev/null
+++ b/src/os/exec/lp_plan9.go
@@ -0,0 +1,72 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $path")
+
+func findExecutable(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	if m := d.Mode(); !m.IsDir() && m&0111 != 0 {
+		return nil
+	}
+	return fs.ErrPermission
+}
+
+// LookPath searches for an executable named file in the
+// directories named by the path environment variable.
+// If file begins with "/", "#", "./", or "../", it is tried
+// directly and the path is not consulted.
+// On success, the result is an absolute path.
+//
+// In older versions of Go, LookPath could return a path relative to the current directory.
+// As of Go 1.19, LookPath will instead return that path along with an error satisfying
+// errors.Is(err, ErrDot). See the package documentation for more details.
+func LookPath(file string) (string, error) {
+	// skip the path lookup for these prefixes
+	skip := []string{"/", "#", "./", "../"}
+
+	for _, p := range skip {
+		if strings.HasPrefix(file, p) {
+			err := findExecutable(file)
+			if err == nil {
+				return file, nil
+			}
+			return "", &Error{file, err}
+		}
+	}
+
+	path := os.Getenv("path")
+	for _, dir := range filepath.SplitList(path) {
+		path := filepath.Join(dir, file)
+		if err := findExecutable(path); err == nil {
+			if !filepath.IsAbs(path) {
+				if execerrdot.Value() != "0" {
+					return path, &Error{file, ErrDot}
+				}
+				execerrdot.IncNonDefault()
+			}
+			return path, nil
+		}
+	}
+	return "", &Error{file, ErrNotFound}
+}
+
+// lookExtensions is a no-op on non-Windows platforms, since
+// they do not restrict executables to specific extensions.
+func lookExtensions(path, dir string) (string, error) {
+	return path, nil
+}
diff --git a/src/os/exec/lp_test.go b/src/os/exec/lp_test.go
new file mode 100644
index 0000000..77d8e84
--- /dev/null
+++ b/src/os/exec/lp_test.go
@@ -0,0 +1,33 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"testing"
+)
+
+var nonExistentPaths = []string{
+	"some-non-existent-path",
+	"non-existent-path/slashed",
+}
+
+func TestLookPathNotFound(t *testing.T) {
+	for _, name := range nonExistentPaths {
+		path, err := LookPath(name)
+		if err == nil {
+			t.Fatalf("LookPath found %q in $PATH", name)
+		}
+		if path != "" {
+			t.Fatalf("LookPath path == %q when err != nil", path)
+		}
+		perr, ok := err.(*Error)
+		if !ok {
+			t.Fatal("LookPath error is not an exec.Error")
+		}
+		if perr.Name != name {
+			t.Fatalf("want Error name %q, got %q", name, perr.Name)
+		}
+	}
+}
diff --git a/src/os/exec/lp_unix.go b/src/os/exec/lp_unix.go
new file mode 100644
index 0000000..3787132
--- /dev/null
+++ b/src/os/exec/lp_unix.go
@@ -0,0 +1,88 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package exec
+
+import (
+	"errors"
+	"internal/syscall/unix"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $PATH")
+
+func findExecutable(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	m := d.Mode()
+	if m.IsDir() {
+		return syscall.EISDIR
+	}
+	err = unix.Eaccess(file, unix.X_OK)
+	// ENOSYS means Eaccess is not available or not implemented.
+	// EPERM can be returned by Linux containers employing seccomp.
+	// In both cases, fall back to checking the permission bits.
+	if err == nil || (err != syscall.ENOSYS && err != syscall.EPERM) {
+		return err
+	}
+	if m&0111 != 0 {
+		return nil
+	}
+	return fs.ErrPermission
+}
+
+// LookPath searches for an executable named file in the
+// directories named by the PATH environment variable.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// Otherwise, on success, the result is an absolute path.
+//
+// In older versions of Go, LookPath could return a path relative to the current directory.
+// As of Go 1.19, LookPath will instead return that path along with an error satisfying
+// errors.Is(err, ErrDot). See the package documentation for more details.
+func LookPath(file string) (string, error) {
+	// NOTE(rsc): I wish we could use the Plan 9 behavior here
+	// (only bypass the path if file begins with / or ./ or ../)
+	// but that would not match all the Unix shells.
+
+	if strings.Contains(file, "/") {
+		err := findExecutable(file)
+		if err == nil {
+			return file, nil
+		}
+		return "", &Error{file, err}
+	}
+	path := os.Getenv("PATH")
+	for _, dir := range filepath.SplitList(path) {
+		if dir == "" {
+			// Unix shell semantics: path element "" means "."
+			dir = "."
+		}
+		path := filepath.Join(dir, file)
+		if err := findExecutable(path); err == nil {
+			if !filepath.IsAbs(path) {
+				if execerrdot.Value() != "0" {
+					return path, &Error{file, ErrDot}
+				}
+				execerrdot.IncNonDefault()
+			}
+			return path, nil
+		}
+	}
+	return "", &Error{file, ErrNotFound}
+}
+
+// lookExtensions is a no-op on non-Windows platforms, since
+// they do not restrict executables to specific extensions.
+func lookExtensions(path, dir string) (string, error) {
+	return path, nil
+}
diff --git a/src/os/exec/lp_unix_test.go b/src/os/exec/lp_unix_test.go
new file mode 100644
index 0000000..1503dda
--- /dev/null
+++ b/src/os/exec/lp_unix_test.go
@@ -0,0 +1,39 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package exec_test
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+)
+
+func TestLookPathUnixEmptyPath(t *testing.T) {
+	// Not parallel: uses Chdir and Setenv.
+
+	tmp := t.TempDir()
+	chdir(t, tmp)
+
+	f, err := os.OpenFile("exec_me", os.O_CREATE|os.O_EXCL, 0700)
+	if err != nil {
+		t.Fatal("OpenFile failed: ", err)
+	}
+	err = f.Close()
+	if err != nil {
+		t.Fatal("Close failed: ", err)
+	}
+
+	t.Setenv("PATH", "")
+
+	path, err := exec.LookPath("exec_me")
+	if err == nil {
+		t.Fatal("LookPath found exec_me in empty $PATH")
+	}
+	if path != "" {
+		t.Fatalf("LookPath path == %q when err != nil", path)
+	}
+}
diff --git a/src/os/exec/lp_wasm.go b/src/os/exec/lp_wasm.go
new file mode 100644
index 0000000..3c81904
--- /dev/null
+++ b/src/os/exec/lp_wasm.go
@@ -0,0 +1,29 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build wasm
+
+package exec
+
+import (
+	"errors"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in $PATH")
+
+// LookPath searches for an executable named file in the
+// directories named by the PATH environment variable.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// The result may be an absolute path or a path relative to the current directory.
+func LookPath(file string) (string, error) {
+	// Wasm can not execute processes, so act as if there are no executables at all.
+	return "", &Error{file, ErrNotFound}
+}
+
+// lookExtensions is a no-op on non-Windows platforms, since
+// they do not restrict executables to specific extensions.
+func lookExtensions(path, dir string) (string, error) {
+	return path, nil
+}
diff --git a/src/os/exec/lp_windows.go b/src/os/exec/lp_windows.go
new file mode 100644
index 0000000..698a97c
--- /dev/null
+++ b/src/os/exec/lp_windows.go
@@ -0,0 +1,212 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package exec
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+)
+
+// ErrNotFound is the error resulting if a path search failed to find an executable file.
+var ErrNotFound = errors.New("executable file not found in %PATH%")
+
+func chkStat(file string) error {
+	d, err := os.Stat(file)
+	if err != nil {
+		return err
+	}
+	if d.IsDir() {
+		return fs.ErrPermission
+	}
+	return nil
+}
+
+func hasExt(file string) bool {
+	i := strings.LastIndex(file, ".")
+	if i < 0 {
+		return false
+	}
+	return strings.LastIndexAny(file, `:\/`) < i
+}
+
+func findExecutable(file string, exts []string) (string, error) {
+	if len(exts) == 0 {
+		return file, chkStat(file)
+	}
+	if hasExt(file) {
+		if chkStat(file) == nil {
+			return file, nil
+		}
+		// Keep checking exts below, so that programs with weird names
+		// like "foo.bat.exe" will resolve instead of failing.
+	}
+	for _, e := range exts {
+		if f := file + e; chkStat(f) == nil {
+			return f, nil
+		}
+	}
+	if hasExt(file) {
+		return "", fs.ErrNotExist
+	}
+	return "", ErrNotFound
+}
+
+// LookPath searches for an executable named file in the
+// directories named by the PATH environment variable.
+// LookPath also uses PATHEXT environment variable to match
+// a suitable candidate.
+// If file contains a slash, it is tried directly and the PATH is not consulted.
+// Otherwise, on success, the result is an absolute path.
+//
+// In older versions of Go, LookPath could return a path relative to the current directory.
+// As of Go 1.19, LookPath will instead return that path along with an error satisfying
+// errors.Is(err, ErrDot). See the package documentation for more details.
+func LookPath(file string) (string, error) {
+	return lookPath(file, pathExt())
+}
+
+// lookExtensions finds windows executable by its dir and path.
+// It uses LookPath to try appropriate extensions.
+// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
+//
+// If the path already has an extension found in PATHEXT,
+// lookExtensions returns it directly without searching
+// for additional extensions. For example,
+// "C:\foo\example.com" would be returned as-is even if the
+// program is actually "C:\foo\example.com.exe".
+func lookExtensions(path, dir string) (string, error) {
+	if filepath.Base(path) == path {
+		path = "." + string(filepath.Separator) + path
+	}
+	exts := pathExt()
+	if ext := filepath.Ext(path); ext != "" {
+		for _, e := range exts {
+			if strings.EqualFold(ext, e) {
+				// Assume that path has already been resolved.
+				return path, nil
+			}
+		}
+	}
+	if dir == "" {
+		return lookPath(path, exts)
+	}
+	if filepath.VolumeName(path) != "" {
+		return lookPath(path, exts)
+	}
+	if len(path) > 1 && os.IsPathSeparator(path[0]) {
+		return lookPath(path, exts)
+	}
+	dirandpath := filepath.Join(dir, path)
+	// We assume that LookPath will only add file extension.
+	lp, err := lookPath(dirandpath, exts)
+	if err != nil {
+		return "", err
+	}
+	ext := strings.TrimPrefix(lp, dirandpath)
+	return path + ext, nil
+}
+
+func pathExt() []string {
+	var exts []string
+	x := os.Getenv(`PATHEXT`)
+	if x != "" {
+		for _, e := range strings.Split(strings.ToLower(x), `;`) {
+			if e == "" {
+				continue
+			}
+			if e[0] != '.' {
+				e = "." + e
+			}
+			exts = append(exts, e)
+		}
+	} else {
+		exts = []string{".com", ".exe", ".bat", ".cmd"}
+	}
+	return exts
+}
+
+// lookPath implements LookPath for the given PATHEXT list.
+func lookPath(file string, exts []string) (string, error) {
+	if strings.ContainsAny(file, `:\/`) {
+		f, err := findExecutable(file, exts)
+		if err == nil {
+			return f, nil
+		}
+		return "", &Error{file, err}
+	}
+
+	// On Windows, creating the NoDefaultCurrentDirectoryInExePath
+	// environment variable (with any value or no value!) signals that
+	// path lookups should skip the current directory.
+	// In theory we are supposed to call NeedCurrentDirectoryForExePathW
+	// "as the registry location of this environment variable can change"
+	// but that seems exceedingly unlikely: it would break all users who
+	// have configured their environment this way!
+	// https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-needcurrentdirectoryforexepathw
+	// See also go.dev/issue/43947.
+	var (
+		dotf   string
+		dotErr error
+	)
+	if _, found := syscall.Getenv("NoDefaultCurrentDirectoryInExePath"); !found {
+		if f, err := findExecutable(filepath.Join(".", file), exts); err == nil {
+			if execerrdot.Value() == "0" {
+				execerrdot.IncNonDefault()
+				return f, nil
+			}
+			dotf, dotErr = f, &Error{file, ErrDot}
+		}
+	}
+
+	path := os.Getenv("path")
+	for _, dir := range filepath.SplitList(path) {
+		if dir == "" {
+			// Skip empty entries, consistent with what PowerShell does.
+			// (See https://go.dev/issue/61493#issuecomment-1649724826.)
+			continue
+		}
+
+		if f, err := findExecutable(filepath.Join(dir, file), exts); err == nil {
+			if dotErr != nil {
+				// https://go.dev/issue/53536: if we resolved a relative path implicitly,
+				// and it is the same executable that would be resolved from the explicit %PATH%,
+				// prefer the explicit name for the executable (and, likely, no error) instead
+				// of the equivalent implicit name with ErrDot.
+				//
+				// Otherwise, return the ErrDot for the implicit path as soon as we find
+				// out that the explicit one doesn't match.
+				dotfi, dotfiErr := os.Lstat(dotf)
+				fi, fiErr := os.Lstat(f)
+				if dotfiErr != nil || fiErr != nil || !os.SameFile(dotfi, fi) {
+					return dotf, dotErr
+				}
+			}
+
+			if !filepath.IsAbs(f) {
+				if execerrdot.Value() != "0" {
+					// If this is the same relative path that we already found,
+					// dotErr is non-nil and we already checked it above.
+					// Otherwise, record this path as the one to which we must resolve,
+					// with or without a dotErr.
+					if dotErr == nil {
+						dotf, dotErr = f, &Error{file, ErrDot}
+					}
+					continue
+				}
+				execerrdot.IncNonDefault()
+			}
+			return f, nil
+		}
+	}
+
+	if dotErr != nil {
+		return dotf, dotErr
+	}
+	return "", &Error{file, ErrNotFound}
+}
diff --git a/src/os/exec/lp_windows_test.go b/src/os/exec/lp_windows_test.go
new file mode 100644
index 0000000..a92a297
--- /dev/null
+++ b/src/os/exec/lp_windows_test.go
@@ -0,0 +1,637 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Use an external test to avoid os/exec -> internal/testenv -> os/exec
+// circular dependency.
+
+package exec_test
+
+import (
+	"errors"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"io/fs"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"slices"
+	"strings"
+	"testing"
+)
+
+func init() {
+	registerHelperCommand("printpath", cmdPrintPath)
+}
+
+func cmdPrintPath(args ...string) {
+	exe, err := os.Executable()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Executable: %v\n", err)
+		os.Exit(1)
+	}
+	fmt.Println(exe)
+}
+
+// makePATH returns a PATH variable referring to the
+// given directories relative to a root directory.
+//
+// The empty string results in an empty entry.
+// Paths beginning with . are kept as relative entries.
+func makePATH(root string, dirs []string) string {
+	paths := make([]string, 0, len(dirs))
+	for _, d := range dirs {
+		switch {
+		case d == "":
+			paths = append(paths, "")
+		case d == "." || (len(d) >= 2 && d[0] == '.' && os.IsPathSeparator(d[1])):
+			paths = append(paths, filepath.Clean(d))
+		default:
+			paths = append(paths, filepath.Join(root, d))
+		}
+	}
+	return strings.Join(paths, string(os.PathListSeparator))
+}
+
+// installProgs creates executable files (or symlinks to executable files) at
+// multiple destination paths. It uses root as prefix for all destination files.
+func installProgs(t *testing.T, root string, files []string) {
+	for _, f := range files {
+		dstPath := filepath.Join(root, f)
+
+		dir := filepath.Dir(dstPath)
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			t.Fatal(err)
+		}
+
+		if os.IsPathSeparator(f[len(f)-1]) {
+			continue // directory and PATH entry only.
+		}
+		if strings.EqualFold(filepath.Ext(f), ".bat") {
+			installBat(t, dstPath)
+		} else {
+			installExe(t, dstPath)
+		}
+	}
+}
+
+// installExe installs a copy of the test executable
+// at the given location, creating directories as needed.
+//
+// (We use a copy instead of just a symlink to ensure that os.Executable
+// always reports an unambiguous path, regardless of how it is implemented.)
+func installExe(t *testing.T, dstPath string) {
+	src, err := os.Open(exePath(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer src.Close()
+
+	dst, err := os.OpenFile(dstPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o777)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := dst.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	_, err = io.Copy(dst, src)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// installBat creates a batch file at dst that prints its own
+// path when run.
+func installBat(t *testing.T, dstPath string) {
+	dst, err := os.OpenFile(dstPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o777)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := dst.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	if _, err := fmt.Fprintf(dst, "@echo %s\r\n", dstPath); err != nil {
+		t.Fatal(err)
+	}
+}
+
+type lookPathTest struct {
+	name            string
+	PATHEXT         string // empty to use default
+	files           []string
+	PATH            []string // if nil, use all parent directories from files
+	searchFor       string
+	want            string
+	wantErr         error
+	skipCmdExeCheck bool // if true, do not check want against the behavior of cmd.exe
+}
+
+var lookPathTests = []lookPathTest{
+	{
+		name:      "first match",
+		files:     []string{`p1\a.exe`, `p2\a.exe`, `p2\a`},
+		searchFor: `a`,
+		want:      `p1\a.exe`,
+	},
+	{
+		name:      "dirs with extensions",
+		files:     []string{`p1.dir\a`, `p2.dir\a.exe`},
+		searchFor: `a`,
+		want:      `p2.dir\a.exe`,
+	},
+	{
+		name:      "first with extension",
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.exe`,
+		want:      `p1\a.exe`,
+	},
+	{
+		name:      "specific name",
+		files:     []string{`p1\a.exe`, `p2\b.exe`},
+		searchFor: `b`,
+		want:      `p2\b.exe`,
+	},
+	{
+		name:      "no extension",
+		files:     []string{`p1\b`, `p2\a`},
+		searchFor: `a`,
+		wantErr:   exec.ErrNotFound,
+	},
+	{
+		name:      "directory, no extension",
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `p2\a`,
+		want:      `p2\a.exe`,
+	},
+	{
+		name:      "no match",
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `b`,
+		wantErr:   exec.ErrNotFound,
+	},
+	{
+		name:      "no match with dir",
+		files:     []string{`p1\b.exe`, `p2\a.exe`},
+		searchFor: `p2\b`,
+		wantErr:   exec.ErrNotFound,
+	},
+	{
+		name:      "extensionless file in CWD ignored",
+		files:     []string{`a`, `p1\a.exe`, `p2\a.exe`},
+		searchFor: `a`,
+		want:      `p1\a.exe`,
+	},
+	{
+		name:      "extensionless file in PATH ignored",
+		files:     []string{`p1\a`, `p2\a.exe`},
+		searchFor: `a`,
+		want:      `p2\a.exe`,
+	},
+	{
+		name:      "specific extension",
+		files:     []string{`p1\a.exe`, `p2\a.bat`},
+		searchFor: `a.bat`,
+		want:      `p2\a.bat`,
+	},
+	{
+		name:      "mismatched extension",
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.com`,
+		wantErr:   exec.ErrNotFound,
+	},
+	{
+		name:      "doubled extension",
+		files:     []string{`p1\a.exe.exe`},
+		searchFor: `a.exe`,
+		want:      `p1\a.exe.exe`,
+	},
+	{
+		name:      "extension not in PATHEXT",
+		PATHEXT:   `.COM;.BAT`,
+		files:     []string{`p1\a.exe`, `p2\a.exe`},
+		searchFor: `a.exe`,
+		want:      `p1\a.exe`,
+	},
+	{
+		name:      "first allowed by PATHEXT",
+		PATHEXT:   `.COM;.EXE`,
+		files:     []string{`p1\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+		want:      `p2\a.exe`,
+	},
+	{
+		name:      "first directory containing a PATHEXT match",
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		files:     []string{`p1\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+		want:      `p1\a.bat`,
+	},
+	{
+		name:      "first PATHEXT entry",
+		PATHEXT:   `.COM;.EXE;.BAT`,
+		files:     []string{`p1\a.bat`, `p1\a.exe`, `p2\a.bat`, `p2\a.exe`},
+		searchFor: `a`,
+		want:      `p1\a.exe`,
+	},
+	{
+		name:      "ignore dir with PATHEXT extension",
+		files:     []string{`a.exe\`},
+		searchFor: `a`,
+		wantErr:   exec.ErrNotFound,
+	},
+	{
+		name:      "ignore empty PATH entry",
+		files:     []string{`a.bat`, `p\a.bat`},
+		PATH:      []string{`p`},
+		searchFor: `a`,
+		want:      `p\a.bat`,
+		// If cmd.exe is too old it might not respect NoDefaultCurrentDirectoryInExePath,
+		// so skip that check.
+		skipCmdExeCheck: true,
+	},
+	{
+		name:      "return ErrDot if found by a different absolute path",
+		files:     []string{`p1\a.bat`, `p2\a.bat`},
+		PATH:      []string{`.\p1`, `p2`},
+		searchFor: `a`,
+		want:      `p1\a.bat`,
+		wantErr:   exec.ErrDot,
+	},
+	{
+		name:      "suppress ErrDot if also found in absolute path",
+		files:     []string{`p1\a.bat`, `p2\a.bat`},
+		PATH:      []string{`.\p1`, `p1`, `p2`},
+		searchFor: `a`,
+		want:      `p1\a.bat`,
+	},
+}
+
+func TestLookPathWindows(t *testing.T) {
+	// Not parallel: uses Chdir and Setenv.
+
+	// We are using the "printpath" command mode to test exec.Command here,
+	// so we won't be calling helperCommand to resolve it.
+	// That may cause it to appear to be unused.
+	maySkipHelperCommand("printpath")
+
+	// Before we begin, find the absolute path to cmd.exe.
+	// In non-short mode, we will use it to check the ground truth
+	// of the test's "want" field.
+	cmdExe, err := exec.LookPath("cmd")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, tt := range lookPathTests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.want == "" && tt.wantErr == nil {
+				t.Fatalf("test must specify either want or wantErr")
+			}
+
+			root := t.TempDir()
+			installProgs(t, root, tt.files)
+
+			if tt.PATHEXT != "" {
+				t.Setenv("PATHEXT", tt.PATHEXT)
+				t.Logf("set PATHEXT=%s", tt.PATHEXT)
+			}
+
+			var pathVar string
+			if tt.PATH == nil {
+				paths := make([]string, 0, len(tt.files))
+				for _, f := range tt.files {
+					dir := filepath.Join(root, filepath.Dir(f))
+					if !slices.Contains(paths, dir) {
+						paths = append(paths, dir)
+					}
+				}
+				pathVar = strings.Join(paths, string(os.PathListSeparator))
+			} else {
+				pathVar = makePATH(root, tt.PATH)
+			}
+			t.Setenv("PATH", pathVar)
+			t.Logf("set PATH=%s", pathVar)
+
+			chdir(t, root)
+
+			if !testing.Short() && !(tt.skipCmdExeCheck || errors.Is(tt.wantErr, exec.ErrDot)) {
+				// Check that cmd.exe, which is our source of ground truth,
+				// agrees that our test case is correct.
+				cmd := testenv.Command(t, cmdExe, "/c", tt.searchFor, "printpath")
+				out, err := cmd.Output()
+				if err == nil {
+					gotAbs := strings.TrimSpace(string(out))
+					wantAbs := ""
+					if tt.want != "" {
+						wantAbs = filepath.Join(root, tt.want)
+					}
+					if gotAbs != wantAbs {
+						// cmd.exe disagrees. Probably the test case is wrong?
+						t.Fatalf("%v\n\tresolved to %s\n\twant %s", cmd, gotAbs, wantAbs)
+					}
+				} else if tt.wantErr == nil {
+					if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
+						t.Fatalf("%v: %v\n%s", cmd, err, ee.Stderr)
+					}
+					t.Fatalf("%v: %v", cmd, err)
+				}
+			}
+
+			got, err := exec.LookPath(tt.searchFor)
+			if filepath.IsAbs(got) {
+				got, err = filepath.Rel(root, got)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+			if got != tt.want {
+				t.Errorf("LookPath(%#q) = %#q; want %#q", tt.searchFor, got, tt.want)
+			}
+			if !errors.Is(err, tt.wantErr) {
+				t.Errorf("LookPath(%#q): %v; want %v", tt.searchFor, err, tt.wantErr)
+			}
+		})
+	}
+}
+
+type commandTest struct {
+	name       string
+	PATH       []string
+	files      []string
+	dir        string
+	arg0       string
+	want       string
+	wantPath   string // the resolved c.Path, if different from want
+	wantErrDot bool
+	wantRunErr error
+}
+
+var commandTests = []commandTest{
+	// testing commands with no slash, like `a.exe`
+	{
+		name:       "current directory",
+		files:      []string{`a.exe`},
+		PATH:       []string{"."},
+		arg0:       `a.exe`,
+		want:       `a.exe`,
+		wantErrDot: true,
+	},
+	{
+		name:       "with extra PATH",
+		files:      []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		PATH:       []string{".", "p2", "p"},
+		arg0:       `a.exe`,
+		want:       `a.exe`,
+		wantErrDot: true,
+	},
+	{
+		name:       "with extra PATH and no extension",
+		files:      []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		PATH:       []string{".", "p2", "p"},
+		arg0:       `a`,
+		want:       `a.exe`,
+		wantErrDot: true,
+	},
+	// testing commands with slash, like `.\a.exe`
+	{
+		name:  "with dir",
+		files: []string{`p\a.exe`},
+		PATH:  []string{"."},
+		arg0:  `p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		name:  "with explicit dot",
+		files: []string{`p\a.exe`},
+		PATH:  []string{"."},
+		arg0:  `.\p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		name:  "with irrelevant PATH",
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		PATH:  []string{".", "p2"},
+		arg0:  `p\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		name:  "with slash and no extension",
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		PATH:  []string{".", "p2"},
+		arg0:  `p\a`,
+		want:  `p\a.exe`,
+	},
+	// tests commands, like `a.exe`, with c.Dir set
+	{
+		// should not find a.exe in p, because LookPath(`a.exe`) will fail when
+		// called by Command (before Dir is set), and that error is sticky.
+		name:       "not found before Dir",
+		files:      []string{`p\a.exe`},
+		PATH:       []string{"."},
+		dir:        `p`,
+		arg0:       `a.exe`,
+		want:       `p\a.exe`,
+		wantRunErr: exec.ErrNotFound,
+	},
+	{
+		// LookPath(`a.exe`) will resolve to `.\a.exe`, but prefixing that with
+		// dir `p\a.exe` will refer to a non-existent file
+		name:       "resolved before Dir",
+		files:      []string{`a.exe`, `p\not_important_file`},
+		PATH:       []string{"."},
+		dir:        `p`,
+		arg0:       `a.exe`,
+		want:       `a.exe`,
+		wantErrDot: true,
+		wantRunErr: fs.ErrNotExist,
+	},
+	{
+		// like above, but making test succeed by installing file
+		// in referred destination (so LookPath(`a.exe`) will still
+		// find `.\a.exe`, but we successfully execute `p\a.exe`)
+		name:       "relative to Dir",
+		files:      []string{`a.exe`, `p\a.exe`},
+		PATH:       []string{"."},
+		dir:        `p`,
+		arg0:       `a.exe`,
+		want:       `p\a.exe`,
+		wantErrDot: true,
+	},
+	{
+		// like above, but add PATH in attempt to break the test
+		name:       "relative to Dir with extra PATH",
+		files:      []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		PATH:       []string{".", "p2", "p"},
+		dir:        `p`,
+		arg0:       `a.exe`,
+		want:       `p\a.exe`,
+		wantErrDot: true,
+	},
+	{
+		// like above, but use "a" instead of "a.exe" for command
+		name:       "relative to Dir with extra PATH and no extension",
+		files:      []string{`a.exe`, `p\a.exe`, `p2\a.exe`},
+		PATH:       []string{".", "p2", "p"},
+		dir:        `p`,
+		arg0:       `a`,
+		want:       `p\a.exe`,
+		wantErrDot: true,
+	},
+	{
+		// finds `a.exe` in the PATH regardless of Dir because Command resolves the
+		// full path (using LookPath) before Dir is set.
+		name:  "from PATH with no match in Dir",
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		PATH:  []string{".", "p2", "p"},
+		dir:   `p`,
+		arg0:  `a.exe`,
+		want:  `p2\a.exe`,
+	},
+	// tests commands, like `.\a.exe`, with c.Dir set
+	{
+		// should use dir when command is path, like ".\a.exe"
+		name:  "relative to Dir with explicit dot",
+		files: []string{`p\a.exe`},
+		PATH:  []string{"."},
+		dir:   `p`,
+		arg0:  `.\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// like above, but with PATH added in attempt to break it
+		name:  "relative to Dir with dot and extra PATH",
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		PATH:  []string{".", "p2"},
+		dir:   `p`,
+		arg0:  `.\a.exe`,
+		want:  `p\a.exe`,
+	},
+	{
+		// LookPath(".\a") will fail before Dir is set, and that error is sticky.
+		name:  "relative to Dir with dot and extra PATH and no extension",
+		files: []string{`p\a.exe`, `p2\a.exe`},
+		PATH:  []string{".", "p2"},
+		dir:   `p`,
+		arg0:  `.\a`,
+		want:  `p\a.exe`,
+	},
+	{
+		// LookPath(".\a") will fail before Dir is set, and that error is sticky.
+		name:  "relative to Dir with different extension",
+		files: []string{`a.exe`, `p\a.bat`},
+		PATH:  []string{"."},
+		dir:   `p`,
+		arg0:  `.\a`,
+		want:  `p\a.bat`,
+	},
+}
+
+func TestCommand(t *testing.T) {
+	// Not parallel: uses Chdir and Setenv.
+
+	// We are using the "printpath" command mode to test exec.Command here,
+	// so we won't be calling helperCommand to resolve it.
+	// That may cause it to appear to be unused.
+	maySkipHelperCommand("printpath")
+
+	for _, tt := range commandTests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.PATH == nil {
+				t.Fatalf("test must specify PATH")
+			}
+
+			root := t.TempDir()
+			installProgs(t, root, tt.files)
+
+			pathVar := makePATH(root, tt.PATH)
+			t.Setenv("PATH", pathVar)
+			t.Logf("set PATH=%s", pathVar)
+
+			chdir(t, root)
+
+			cmd := exec.Command(tt.arg0, "printpath")
+			cmd.Dir = filepath.Join(root, tt.dir)
+			if tt.wantErrDot {
+				if errors.Is(cmd.Err, exec.ErrDot) {
+					cmd.Err = nil
+				} else {
+					t.Fatalf("cmd.Err = %v; want ErrDot", cmd.Err)
+				}
+			}
+
+			out, err := cmd.Output()
+			if err != nil {
+				if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
+					t.Logf("%v: %v\n%s", cmd, err, ee.Stderr)
+				} else {
+					t.Logf("%v: %v", cmd, err)
+				}
+				if !errors.Is(err, tt.wantRunErr) {
+					t.Errorf("want %v", tt.wantRunErr)
+				}
+				return
+			}
+
+			got := strings.TrimSpace(string(out))
+			if filepath.IsAbs(got) {
+				got, err = filepath.Rel(root, got)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+			if got != tt.want {
+				t.Errorf("\nran  %#q\nwant %#q", got, tt.want)
+			}
+
+			gotPath := cmd.Path
+			wantPath := tt.wantPath
+			if wantPath == "" {
+				if strings.Contains(tt.arg0, `\`) {
+					wantPath = tt.arg0
+				} else if tt.wantErrDot {
+					wantPath = strings.TrimPrefix(tt.want, tt.dir+`\`)
+				} else {
+					wantPath = filepath.Join(root, tt.want)
+				}
+			}
+			if gotPath != wantPath {
+				t.Errorf("\ncmd.Path = %#q\nwant       %#q", gotPath, wantPath)
+			}
+		})
+	}
+}
+
+func TestAbsCommandWithDoubledExtension(t *testing.T) {
+	t.Parallel()
+
+	// We expect that ".com" is always included in PATHEXT, but it may also be
+	// found in the import path of a Go package. If it is at the root of the
+	// import path, the resulting executable may be named like "example.com.exe".
+	//
+	// Since "example.com" looks like a proper executable name, it is probably ok
+	// for exec.Command to try to run it directly without re-resolving it.
+	// However, exec.LookPath should try a little harder to figure it out.
+
+	comPath := filepath.Join(t.TempDir(), "example.com")
+	batPath := comPath + ".bat"
+	installBat(t, batPath)
+
+	cmd := exec.Command(comPath)
+	out, err := cmd.CombinedOutput()
+	t.Logf("%v: %v\n%s", cmd, err, out)
+	if !errors.Is(err, fs.ErrNotExist) {
+		t.Errorf("Command(%#q).Run: %v\nwant fs.ErrNotExist", comPath, err)
+	}
+
+	resolved, err := exec.LookPath(comPath)
+	if err != nil || resolved != batPath {
+		t.Fatalf("LookPath(%#q) = %v, %v; want %#q, <nil>", comPath, resolved, err, batPath)
+	}
+}
diff --git a/src/os/exec/read3.go b/src/os/exec/read3.go
new file mode 100644
index 0000000..8327d73
--- /dev/null
+++ b/src/os/exec/read3.go
@@ -0,0 +1,91 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+
+// This is a test program that verifies that it can read from
+// descriptor 3 and that no other descriptors are open.
+// This is not done via TestHelperProcess and GO_EXEC_TEST_PID
+// because we want to ensure that this program does not use cgo,
+// because C libraries can open file descriptors behind our backs
+// and confuse the test. See issue 25628.
+package main
+
+import (
+	"fmt"
+	"internal/poll"
+	"io"
+	"os"
+	"os/exec"
+	"os/exec/internal/fdtest"
+	"runtime"
+	"strings"
+)
+
+func main() {
+	fd3 := os.NewFile(3, "fd3")
+	defer fd3.Close()
+
+	bs, err := io.ReadAll(fd3)
+	if err != nil {
+		fmt.Printf("ReadAll from fd 3: %v\n", err)
+		os.Exit(1)
+	}
+
+	// Now verify that there are no other open fds.
+	// stdin == 0
+	// stdout == 1
+	// stderr == 2
+	// descriptor from parent == 3
+	// All descriptors 4 and up should be available,
+	// except for any used by the network poller.
+	for fd := uintptr(4); fd <= 100; fd++ {
+		if poll.IsPollDescriptor(fd) {
+			continue
+		}
+
+		if !fdtest.Exists(fd) {
+			continue
+		}
+
+		fmt.Printf("leaked parent file. fdtest.Exists(%d) got true want false\n", fd)
+
+		fdfile := fmt.Sprintf("/proc/self/fd/%d", fd)
+		link, err := os.Readlink(fdfile)
+		fmt.Printf("readlink(%q) = %q, %v\n", fdfile, link, err)
+
+		var args []string
+		switch runtime.GOOS {
+		case "plan9":
+			args = []string{fmt.Sprintf("/proc/%d/fd", os.Getpid())}
+		case "aix", "solaris", "illumos":
+			args = []string{fmt.Sprint(os.Getpid())}
+		default:
+			args = []string{"-p", fmt.Sprint(os.Getpid())}
+		}
+
+		// Determine which command to use to display open files.
+		ofcmd := "lsof"
+		switch runtime.GOOS {
+		case "dragonfly", "freebsd", "netbsd", "openbsd":
+			ofcmd = "fstat"
+		case "plan9":
+			ofcmd = "/bin/cat"
+		case "aix":
+			ofcmd = "procfiles"
+		case "solaris", "illumos":
+			ofcmd = "pfiles"
+		}
+
+		cmd := exec.Command(ofcmd, args...)
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%s failed: %v\n", strings.Join(cmd.Args, " "), err)
+		}
+		fmt.Printf("%s", out)
+		os.Exit(1)
+	}
+
+	os.Stdout.Write(bs)
+}
diff --git a/src/os/exec_plan9.go b/src/os/exec_plan9.go
new file mode 100644
index 0000000..69714ff
--- /dev/null
+++ b/src/os/exec_plan9.go
@@ -0,0 +1,149 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"internal/itoa"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+// The only signal values guaranteed to be present in the os package
+// on all systems are Interrupt (send the process an interrupt) and
+// Kill (force the process to exit). Interrupt is not implemented on
+// Windows; using it with os.Process.Signal will return an error.
+var (
+	Interrupt Signal = syscall.Note("interrupt")
+	Kill      Signal = syscall.Note("kill")
+)
+
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	sysattr := &syscall.ProcAttr{
+		Dir: attr.Dir,
+		Env: attr.Env,
+		Sys: attr.Sys,
+	}
+
+	sysattr.Files = make([]uintptr, 0, len(attr.Files))
+	for _, f := range attr.Files {
+		sysattr.Files = append(sysattr.Files, f.Fd())
+	}
+
+	pid, h, e := syscall.StartProcess(name, argv, sysattr)
+	if e != nil {
+		return nil, &PathError{Op: "fork/exec", Path: name, Err: e}
+	}
+
+	return newProcess(pid, h), nil
+}
+
+func (p *Process) writeProcFile(file string, data string) error {
+	f, e := OpenFile("/proc/"+itoa.Itoa(p.Pid)+"/"+file, O_WRONLY, 0)
+	if e != nil {
+		return e
+	}
+	defer f.Close()
+	_, e = f.Write([]byte(data))
+	return e
+}
+
+func (p *Process) signal(sig Signal) error {
+	if p.done() {
+		return ErrProcessDone
+	}
+	if e := p.writeProcFile("note", sig.String()); e != nil {
+		return NewSyscallError("signal", e)
+	}
+	return nil
+}
+
+func (p *Process) kill() error {
+	return p.signal(Kill)
+}
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	var waitmsg syscall.Waitmsg
+
+	if p.Pid == -1 {
+		return nil, ErrInvalid
+	}
+	err = syscall.WaitProcess(p.Pid, &waitmsg)
+	if err != nil {
+		return nil, NewSyscallError("wait", err)
+	}
+
+	p.setDone()
+	ps = &ProcessState{
+		pid:    waitmsg.Pid,
+		status: &waitmsg,
+	}
+	return ps, nil
+}
+
+func (p *Process) release() error {
+	// NOOP for Plan 9.
+	p.Pid = -1
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	// NOOP for Plan 9.
+	return newProcess(pid, 0), nil
+}
+
+// ProcessState stores information about a process, as reported by Wait.
+type ProcessState struct {
+	pid    int              // The process's id.
+	status *syscall.Waitmsg // System-dependent status info.
+}
+
+// Pid returns the process id of the exited process.
+func (p *ProcessState) Pid() int {
+	return p.pid
+}
+
+func (p *ProcessState) exited() bool {
+	return p.status.Exited()
+}
+
+func (p *ProcessState) success() bool {
+	return p.status.ExitStatus() == 0
+}
+
+func (p *ProcessState) sys() any {
+	return p.status
+}
+
+func (p *ProcessState) sysUsage() any {
+	return p.status
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return time.Duration(p.status.Time[0]) * time.Millisecond
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return time.Duration(p.status.Time[1]) * time.Millisecond
+}
+
+func (p *ProcessState) String() string {
+	if p == nil {
+		return "<nil>"
+	}
+	return "exit status: " + p.status.Msg
+}
+
+// ExitCode returns the exit code of the exited process, or -1
+// if the process hasn't exited or was terminated by a signal.
+func (p *ProcessState) ExitCode() int {
+	// return -1 if the process hasn't started.
+	if p == nil {
+		return -1
+	}
+	return p.status.ExitStatus()
+}
diff --git a/src/os/exec_posix.go b/src/os/exec_posix.go
new file mode 100644
index 0000000..4f9ea08
--- /dev/null
+++ b/src/os/exec_posix.go
@@ -0,0 +1,136 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix || (js && wasm) || wasip1 || windows
+
+package os
+
+import (
+	"internal/itoa"
+	"internal/syscall/execenv"
+	"runtime"
+	"syscall"
+)
+
+// The only signal values guaranteed to be present in the os package on all
+// systems are os.Interrupt (send the process an interrupt) and os.Kill (force
+// the process to exit). On Windows, sending os.Interrupt to a process with
+// os.Process.Signal is not implemented; it will return an error instead of
+// sending a signal.
+var (
+	Interrupt Signal = syscall.SIGINT
+	Kill      Signal = syscall.SIGKILL
+)
+
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	// If there is no SysProcAttr (ie. no Chroot or changed
+	// UID/GID), double-check existence of the directory we want
+	// to chdir into. We can make the error clearer this way.
+	if attr != nil && attr.Sys == nil && attr.Dir != "" {
+		if _, err := Stat(attr.Dir); err != nil {
+			pe := err.(*PathError)
+			pe.Op = "chdir"
+			return nil, pe
+		}
+	}
+
+	sysattr := &syscall.ProcAttr{
+		Dir: attr.Dir,
+		Env: attr.Env,
+		Sys: attr.Sys,
+	}
+	if sysattr.Env == nil {
+		sysattr.Env, err = execenv.Default(sysattr.Sys)
+		if err != nil {
+			return nil, err
+		}
+	}
+	sysattr.Files = make([]uintptr, 0, len(attr.Files))
+	for _, f := range attr.Files {
+		sysattr.Files = append(sysattr.Files, f.Fd())
+	}
+
+	pid, h, e := syscall.StartProcess(name, argv, sysattr)
+
+	// Make sure we don't run the finalizers of attr.Files.
+	runtime.KeepAlive(attr)
+
+	if e != nil {
+		return nil, &PathError{Op: "fork/exec", Path: name, Err: e}
+	}
+
+	return newProcess(pid, h), nil
+}
+
+func (p *Process) kill() error {
+	return p.Signal(Kill)
+}
+
+// ProcessState stores information about a process, as reported by Wait.
+type ProcessState struct {
+	pid    int                // The process's id.
+	status syscall.WaitStatus // System-dependent status info.
+	rusage *syscall.Rusage
+}
+
+// Pid returns the process id of the exited process.
+func (p *ProcessState) Pid() int {
+	return p.pid
+}
+
+func (p *ProcessState) exited() bool {
+	return p.status.Exited()
+}
+
+func (p *ProcessState) success() bool {
+	return p.status.ExitStatus() == 0
+}
+
+func (p *ProcessState) sys() any {
+	return p.status
+}
+
+func (p *ProcessState) sysUsage() any {
+	return p.rusage
+}
+
+func (p *ProcessState) String() string {
+	if p == nil {
+		return "<nil>"
+	}
+	status := p.Sys().(syscall.WaitStatus)
+	res := ""
+	switch {
+	case status.Exited():
+		code := status.ExitStatus()
+		if runtime.GOOS == "windows" && uint(code) >= 1<<16 { // windows uses large hex numbers
+			res = "exit status " + itoa.Uitox(uint(code))
+		} else { // unix systems use small decimal integers
+			res = "exit status " + itoa.Itoa(code) // unix
+		}
+	case status.Signaled():
+		res = "signal: " + status.Signal().String()
+	case status.Stopped():
+		res = "stop signal: " + status.StopSignal().String()
+		if status.StopSignal() == syscall.SIGTRAP && status.TrapCause() != 0 {
+			res += " (trap " + itoa.Itoa(status.TrapCause()) + ")"
+		}
+	case status.Continued():
+		res = "continued"
+	}
+	if status.CoreDump() {
+		res += " (core dumped)"
+	}
+	return res
+}
+
+// ExitCode returns the exit code of the exited process, or -1
+// if the process hasn't exited or was terminated by a signal.
+func (p *ProcessState) ExitCode() int {
+	// return -1 if the process hasn't started.
+	if p == nil {
+		return -1
+	}
+	return p.status.ExitStatus()
+}
diff --git a/src/os/exec_unix.go b/src/os/exec_unix.go
new file mode 100644
index 0000000..36b320d
--- /dev/null
+++ b/src/os/exec_unix.go
@@ -0,0 +1,104 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix || (js && wasm) || wasip1
+
+package os
+
+import (
+	"errors"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	if p.Pid == -1 {
+		return nil, syscall.EINVAL
+	}
+
+	// If we can block until Wait4 will succeed immediately, do so.
+	ready, err := p.blockUntilWaitable()
+	if err != nil {
+		return nil, err
+	}
+	if ready {
+		// Mark the process done now, before the call to Wait4,
+		// so that Process.signal will not send a signal.
+		p.setDone()
+		// Acquire a write lock on sigMu to wait for any
+		// active call to the signal method to complete.
+		p.sigMu.Lock()
+		p.sigMu.Unlock()
+	}
+
+	var (
+		status syscall.WaitStatus
+		rusage syscall.Rusage
+		pid1   int
+		e      error
+	)
+	for {
+		pid1, e = syscall.Wait4(p.Pid, &status, 0, &rusage)
+		if e != syscall.EINTR {
+			break
+		}
+	}
+	if e != nil {
+		return nil, NewSyscallError("wait", e)
+	}
+	p.setDone()
+	ps = &ProcessState{
+		pid:    pid1,
+		status: status,
+		rusage: &rusage,
+	}
+	return ps, nil
+}
+
+func (p *Process) signal(sig Signal) error {
+	if p.Pid == -1 {
+		return errors.New("os: process already released")
+	}
+	if p.Pid == 0 {
+		return errors.New("os: process not initialized")
+	}
+	p.sigMu.RLock()
+	defer p.sigMu.RUnlock()
+	if p.done() {
+		return ErrProcessDone
+	}
+	s, ok := sig.(syscall.Signal)
+	if !ok {
+		return errors.New("os: unsupported signal type")
+	}
+	if e := syscall.Kill(p.Pid, s); e != nil {
+		if e == syscall.ESRCH {
+			return ErrProcessDone
+		}
+		return e
+	}
+	return nil
+}
+
+func (p *Process) release() error {
+	// NOOP for unix.
+	p.Pid = -1
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	// NOOP for unix.
+	return newProcess(pid, 0), nil
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return time.Duration(p.rusage.Utime.Nano()) * time.Nanosecond
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return time.Duration(p.rusage.Stime.Nano()) * time.Nanosecond
+}
diff --git a/src/os/exec_unix_test.go b/src/os/exec_unix_test.go
new file mode 100644
index 0000000..88e1b63
--- /dev/null
+++ b/src/os/exec_unix_test.go
@@ -0,0 +1,45 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package os_test
+
+import (
+	"internal/testenv"
+	. "os"
+	"syscall"
+	"testing"
+)
+
+func TestErrProcessDone(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	t.Parallel()
+
+	p, err := StartProcess(testenv.GoToolPath(t), []string{"go"}, &ProcAttr{})
+	if err != nil {
+		t.Fatalf("starting test process: %v", err)
+	}
+	p.Wait()
+	if got := p.Signal(Kill); got != ErrProcessDone {
+		t.Errorf("got %v want %v", got, ErrProcessDone)
+	}
+}
+
+func TestUNIXProcessAlive(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	t.Parallel()
+
+	p, err := StartProcess(testenv.GoToolPath(t), []string{"sleep", "1"}, &ProcAttr{})
+	if err != nil {
+		t.Skipf("starting test process: %v", err)
+	}
+	defer p.Kill()
+
+	proc, _ := FindProcess(p.Pid)
+	err = proc.Signal(syscall.Signal(0))
+	if err != nil {
+		t.Errorf("OS reported error for running process: %v", err)
+	}
+}
diff --git a/src/os/exec_windows.go b/src/os/exec_windows.go
new file mode 100644
index 0000000..061a12b
--- /dev/null
+++ b/src/os/exec_windows.go
@@ -0,0 +1,175 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"errors"
+	"internal/syscall/windows"
+	"runtime"
+	"sync/atomic"
+	"syscall"
+	"time"
+)
+
+func (p *Process) wait() (ps *ProcessState, err error) {
+	handle := atomic.LoadUintptr(&p.handle)
+	s, e := syscall.WaitForSingleObject(syscall.Handle(handle), syscall.INFINITE)
+	switch s {
+	case syscall.WAIT_OBJECT_0:
+		break
+	case syscall.WAIT_FAILED:
+		return nil, NewSyscallError("WaitForSingleObject", e)
+	default:
+		return nil, errors.New("os: unexpected result from WaitForSingleObject")
+	}
+	var ec uint32
+	e = syscall.GetExitCodeProcess(syscall.Handle(handle), &ec)
+	if e != nil {
+		return nil, NewSyscallError("GetExitCodeProcess", e)
+	}
+	var u syscall.Rusage
+	e = syscall.GetProcessTimes(syscall.Handle(handle), &u.CreationTime, &u.ExitTime, &u.KernelTime, &u.UserTime)
+	if e != nil {
+		return nil, NewSyscallError("GetProcessTimes", e)
+	}
+	p.setDone()
+	defer p.Release()
+	return &ProcessState{p.Pid, syscall.WaitStatus{ExitCode: ec}, &u}, nil
+}
+
+func (p *Process) signal(sig Signal) error {
+	handle := atomic.LoadUintptr(&p.handle)
+	if handle == uintptr(syscall.InvalidHandle) {
+		return syscall.EINVAL
+	}
+	if p.done() {
+		return ErrProcessDone
+	}
+	if sig == Kill {
+		var terminationHandle syscall.Handle
+		e := syscall.DuplicateHandle(^syscall.Handle(0), syscall.Handle(handle), ^syscall.Handle(0), &terminationHandle, syscall.PROCESS_TERMINATE, false, 0)
+		if e != nil {
+			return NewSyscallError("DuplicateHandle", e)
+		}
+		runtime.KeepAlive(p)
+		defer syscall.CloseHandle(terminationHandle)
+		e = syscall.TerminateProcess(syscall.Handle(terminationHandle), 1)
+		return NewSyscallError("TerminateProcess", e)
+	}
+	// TODO(rsc): Handle Interrupt too?
+	return syscall.Errno(syscall.EWINDOWS)
+}
+
+func (p *Process) release() error {
+	handle := atomic.SwapUintptr(&p.handle, uintptr(syscall.InvalidHandle))
+	if handle == uintptr(syscall.InvalidHandle) {
+		return syscall.EINVAL
+	}
+	e := syscall.CloseHandle(syscall.Handle(handle))
+	if e != nil {
+		return NewSyscallError("CloseHandle", e)
+	}
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+func findProcess(pid int) (p *Process, err error) {
+	const da = syscall.STANDARD_RIGHTS_READ |
+		syscall.PROCESS_QUERY_INFORMATION | syscall.SYNCHRONIZE
+	h, e := syscall.OpenProcess(da, false, uint32(pid))
+	if e != nil {
+		return nil, NewSyscallError("OpenProcess", e)
+	}
+	return newProcess(pid, uintptr(h)), nil
+}
+
+func init() {
+	cmd := windows.UTF16PtrToString(syscall.GetCommandLine())
+	if len(cmd) == 0 {
+		arg0, _ := Executable()
+		Args = []string{arg0}
+	} else {
+		Args = commandLineToArgv(cmd)
+	}
+}
+
+// appendBSBytes appends n '\\' bytes to b and returns the resulting slice.
+func appendBSBytes(b []byte, n int) []byte {
+	for ; n > 0; n-- {
+		b = append(b, '\\')
+	}
+	return b
+}
+
+// readNextArg splits command line string cmd into next
+// argument and command line remainder.
+func readNextArg(cmd string) (arg []byte, rest string) {
+	var b []byte
+	var inquote bool
+	var nslash int
+	for ; len(cmd) > 0; cmd = cmd[1:] {
+		c := cmd[0]
+		switch c {
+		case ' ', '\t':
+			if !inquote {
+				return appendBSBytes(b, nslash), cmd[1:]
+			}
+		case '"':
+			b = appendBSBytes(b, nslash/2)
+			if nslash%2 == 0 {
+				// use "Prior to 2008" rule from
+				// http://daviddeley.com/autohotkey/parameters/parameters.htm
+				// section 5.2 to deal with double double quotes
+				if inquote && len(cmd) > 1 && cmd[1] == '"' {
+					b = append(b, c)
+					cmd = cmd[1:]
+				}
+				inquote = !inquote
+			} else {
+				b = append(b, c)
+			}
+			nslash = 0
+			continue
+		case '\\':
+			nslash++
+			continue
+		}
+		b = appendBSBytes(b, nslash)
+		nslash = 0
+		b = append(b, c)
+	}
+	return appendBSBytes(b, nslash), ""
+}
+
+// commandLineToArgv splits a command line into individual argument
+// strings, following the Windows conventions documented
+// at http://daviddeley.com/autohotkey/parameters/parameters.htm#WINARGV
+func commandLineToArgv(cmd string) []string {
+	var args []string
+	for len(cmd) > 0 {
+		if cmd[0] == ' ' || cmd[0] == '\t' {
+			cmd = cmd[1:]
+			continue
+		}
+		var arg []byte
+		arg, cmd = readNextArg(cmd)
+		args = append(args, string(arg))
+	}
+	return args
+}
+
+func ftToDuration(ft *syscall.Filetime) time.Duration {
+	n := int64(ft.HighDateTime)<<32 + int64(ft.LowDateTime) // in 100-nanosecond intervals
+	return time.Duration(n*100) * time.Nanosecond
+}
+
+func (p *ProcessState) userTime() time.Duration {
+	return ftToDuration(&p.rusage.UserTime)
+}
+
+func (p *ProcessState) systemTime() time.Duration {
+	return ftToDuration(&p.rusage.KernelTime)
+}
diff --git a/src/os/exec_windows_test.go b/src/os/exec_windows_test.go
new file mode 100644
index 0000000..f8ed4cd
--- /dev/null
+++ b/src/os/exec_windows_test.go
@@ -0,0 +1,83 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build windows
+
+package os_test
+
+import (
+	"internal/testenv"
+	"io"
+	. "os"
+	"path/filepath"
+	"sync"
+	"testing"
+)
+
+func TestRemoveAllWithExecutedProcess(t *testing.T) {
+	// Regression test for golang.org/issue/25965.
+	if testing.Short() {
+		t.Skip("slow test; skipping")
+	}
+	testenv.MustHaveExec(t)
+
+	name, err := Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+	r, err := Open(name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+	const n = 100
+	var execs [n]string
+	// First create n executables.
+	for i := 0; i < n; i++ {
+		// Rewind r.
+		if _, err := r.Seek(0, io.SeekStart); err != nil {
+			t.Fatal(err)
+		}
+		name := filepath.Join(t.TempDir(), "test.exe")
+		execs[i] = name
+		w, err := Create(name)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err = io.Copy(w, r); err != nil {
+			w.Close()
+			t.Fatal(err)
+		}
+		if err := w.Sync(); err != nil {
+			w.Close()
+			t.Fatal(err)
+		}
+		if err = w.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}
+	// Then run each executable and remove its directory.
+	// Run each executable in a separate goroutine to add some load
+	// and increase the chance of triggering the bug.
+	var wg sync.WaitGroup
+	wg.Add(n)
+	for i := 0; i < n; i++ {
+		go func(i int) {
+			defer wg.Done()
+			name := execs[i]
+			dir := filepath.Dir(name)
+			// Run test.exe without executing any test, just to make it do something.
+			cmd := testenv.Command(t, name, "-test.run=^$")
+			if err := cmd.Run(); err != nil {
+				t.Errorf("exec failed: %v", err)
+			}
+			// Remove dir and check that it doesn't return `ERROR_ACCESS_DENIED`.
+			err = RemoveAll(dir)
+			if err != nil {
+				t.Errorf("RemoveAll failed: %v", err)
+			}
+		}(i)
+	}
+	wg.Wait()
+}
diff --git a/src/os/executable.go b/src/os/executable.go
new file mode 100644
index 0000000..cc3134a
--- /dev/null
+++ b/src/os/executable.go
@@ -0,0 +1,20 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+// Executable returns the path name for the executable that started
+// the current process. There is no guarantee that the path is still
+// pointing to the correct executable. If a symlink was used to start
+// the process, depending on the operating system, the result might
+// be the symlink or the path it pointed to. If a stable result is
+// needed, path/filepath.EvalSymlinks might help.
+//
+// Executable returns an absolute path unless an error occurred.
+//
+// The main use case is finding resources located relative to an
+// executable.
+func Executable() (string, error) {
+	return executable()
+}
diff --git a/src/os/executable_darwin.go b/src/os/executable_darwin.go
new file mode 100644
index 0000000..dae9f4e
--- /dev/null
+++ b/src/os/executable_darwin.go
@@ -0,0 +1,29 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import "errors"
+
+var executablePath string // set by ../runtime/os_darwin.go
+
+var initCwd, initCwdErr = Getwd()
+
+func executable() (string, error) {
+	ep := executablePath
+	if len(ep) == 0 {
+		return ep, errors.New("cannot find executable path")
+	}
+	if ep[0] != '/' {
+		if initCwdErr != nil {
+			return ep, initCwdErr
+		}
+		if len(ep) > 2 && ep[0:2] == "./" {
+			// skip "./"
+			ep = ep[2:]
+		}
+		ep = initCwd + "/" + ep
+	}
+	return ep, nil
+}
diff --git a/src/os/executable_dragonfly.go b/src/os/executable_dragonfly.go
new file mode 100644
index 0000000..19c2ae8
--- /dev/null
+++ b/src/os/executable_dragonfly.go
@@ -0,0 +1,12 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+// From DragonFly's <sys/sysctl.h>
+const (
+	_CTL_KERN           = 1
+	_KERN_PROC          = 14
+	_KERN_PROC_PATHNAME = 9
+)
diff --git a/src/os/executable_freebsd.go b/src/os/executable_freebsd.go
new file mode 100644
index 0000000..95f1a93
--- /dev/null
+++ b/src/os/executable_freebsd.go
@@ -0,0 +1,12 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+// From FreeBSD's <sys/sysctl.h>
+const (
+	_CTL_KERN           = 1
+	_KERN_PROC          = 14
+	_KERN_PROC_PATHNAME = 12
+)
diff --git a/src/os/executable_path.go b/src/os/executable_path.go
new file mode 100644
index 0000000..d6161bc
--- /dev/null
+++ b/src/os/executable_path.go
@@ -0,0 +1,104 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build aix || openbsd
+
+package os
+
+// We query the working directory at init, to use it later to search for the
+// executable file
+// errWd will be checked later, if we need to use initWd
+var initWd, errWd = Getwd()
+
+func executable() (string, error) {
+	var exePath string
+	if len(Args) == 0 || Args[0] == "" {
+		return "", ErrNotExist
+	}
+	if IsPathSeparator(Args[0][0]) {
+		// Args[0] is an absolute path, so it is the executable.
+		// Note that we only need to worry about Unix paths here.
+		exePath = Args[0]
+	} else {
+		for i := 1; i < len(Args[0]); i++ {
+			if IsPathSeparator(Args[0][i]) {
+				// Args[0] is a relative path: prepend the
+				// initial working directory.
+				if errWd != nil {
+					return "", errWd
+				}
+				exePath = initWd + string(PathSeparator) + Args[0]
+				break
+			}
+		}
+	}
+	if exePath != "" {
+		if err := isExecutable(exePath); err != nil {
+			return "", err
+		}
+		return exePath, nil
+	}
+	// Search for executable in $PATH.
+	for _, dir := range splitPathList(Getenv("PATH")) {
+		if len(dir) == 0 {
+			dir = "."
+		}
+		if !IsPathSeparator(dir[0]) {
+			if errWd != nil {
+				return "", errWd
+			}
+			dir = initWd + string(PathSeparator) + dir
+		}
+		exePath = dir + string(PathSeparator) + Args[0]
+		switch isExecutable(exePath) {
+		case nil:
+			return exePath, nil
+		case ErrPermission:
+			return "", ErrPermission
+		}
+	}
+	return "", ErrNotExist
+}
+
+// isExecutable returns an error if a given file is not an executable.
+func isExecutable(path string) error {
+	stat, err := Stat(path)
+	if err != nil {
+		return err
+	}
+	mode := stat.Mode()
+	if !mode.IsRegular() {
+		return ErrPermission
+	}
+	if (mode & 0111) == 0 {
+		return ErrPermission
+	}
+	return nil
+}
+
+// splitPathList splits a path list.
+// This is based on genSplit from strings/strings.go
+func splitPathList(pathList string) []string {
+	if pathList == "" {
+		return nil
+	}
+	n := 1
+	for i := 0; i < len(pathList); i++ {
+		if pathList[i] == PathListSeparator {
+			n++
+		}
+	}
+	start := 0
+	a := make([]string, n)
+	na := 0
+	for i := 0; i+1 <= len(pathList) && na+1 < n; i++ {
+		if pathList[i] == PathListSeparator {
+			a[na] = pathList[start:i]
+			na++
+			start = i + 1
+		}
+	}
+	a[na] = pathList[start:]
+	return a[:na+1]
+}
diff --git a/src/os/executable_plan9.go b/src/os/executable_plan9.go
new file mode 100644
index 0000000..8d8c832
--- /dev/null
+++ b/src/os/executable_plan9.go
@@ -0,0 +1,22 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build plan9
+
+package os
+
+import (
+	"internal/itoa"
+	"syscall"
+)
+
+func executable() (string, error) {
+	fn := "/proc/" + itoa.Itoa(Getpid()) + "/text"
+	f, err := Open(fn)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	return syscall.Fd2path(int(f.Fd()))
+}
diff --git a/src/os/executable_procfs.go b/src/os/executable_procfs.go
new file mode 100644
index 0000000..94e674e
--- /dev/null
+++ b/src/os/executable_procfs.go
@@ -0,0 +1,37 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux || netbsd
+
+package os
+
+import (
+	"errors"
+	"runtime"
+)
+
+func executable() (string, error) {
+	var procfn string
+	switch runtime.GOOS {
+	default:
+		return "", errors.New("Executable not implemented for " + runtime.GOOS)
+	case "linux", "android":
+		procfn = "/proc/self/exe"
+	case "netbsd":
+		procfn = "/proc/curproc/exe"
+	}
+	path, err := Readlink(procfn)
+
+	// When the executable has been deleted then Readlink returns a
+	// path appended with " (deleted)".
+	return stringsTrimSuffix(path, " (deleted)"), err
+}
+
+// stringsTrimSuffix is the same as strings.TrimSuffix.
+func stringsTrimSuffix(s, suffix string) string {
+	if len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix {
+		return s[:len(s)-len(suffix)]
+	}
+	return s
+}
diff --git a/src/os/executable_solaris.go b/src/os/executable_solaris.go
new file mode 100644
index 0000000..b145980
--- /dev/null
+++ b/src/os/executable_solaris.go
@@ -0,0 +1,32 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import "syscall"
+
+var executablePath string // set by sysauxv in ../runtime/os3_solaris.go
+
+var initCwd, initCwdErr = Getwd()
+
+func executable() (string, error) {
+	path := executablePath
+	if len(path) == 0 {
+		path, err := syscall.Getexecname()
+		if err != nil {
+			return path, err
+		}
+	}
+	if len(path) > 0 && path[0] != '/' {
+		if initCwdErr != nil {
+			return path, initCwdErr
+		}
+		if len(path) > 2 && path[0:2] == "./" {
+			// skip "./"
+			path = path[2:]
+		}
+		return initCwd + "/" + path, nil
+	}
+	return path, nil
+}
diff --git a/src/os/executable_sysctl.go b/src/os/executable_sysctl.go
new file mode 100644
index 0000000..3c2aeac
--- /dev/null
+++ b/src/os/executable_sysctl.go
@@ -0,0 +1,35 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build freebsd || dragonfly
+
+package os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func executable() (string, error) {
+	mib := [4]int32{_CTL_KERN, _KERN_PROC, _KERN_PROC_PATHNAME, -1}
+
+	n := uintptr(0)
+	// get length
+	_, _, err := syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, 0, uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	buf := make([]byte, n)
+	_, _, err = syscall.Syscall6(syscall.SYS___SYSCTL, uintptr(unsafe.Pointer(&mib[0])), 4, uintptr(unsafe.Pointer(&buf[0])), uintptr(unsafe.Pointer(&n)), 0, 0)
+	if err != 0 {
+		return "", err
+	}
+	if n == 0 { // shouldn't happen
+		return "", nil
+	}
+	return string(buf[:n-1]), nil
+}
diff --git a/src/os/executable_test.go b/src/os/executable_test.go
new file mode 100644
index 0000000..98b72d7
--- /dev/null
+++ b/src/os/executable_test.go
@@ -0,0 +1,155 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	"fmt"
+	"internal/testenv"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+const executable_EnvVar = "OSTEST_OUTPUT_EXECPATH"
+
+func TestExecutable(t *testing.T) {
+	testenv.MustHaveExec(t)
+	t.Parallel()
+
+	ep, err := os.Executable()
+	if err != nil {
+		t.Fatalf("Executable failed: %v", err)
+	}
+	// we want fn to be of the form "dir/prog"
+	dir := filepath.Dir(filepath.Dir(ep))
+	fn, err := filepath.Rel(dir, ep)
+	if err != nil {
+		t.Fatalf("filepath.Rel: %v", err)
+	}
+
+	cmd := testenv.Command(t, fn, "-test.run=^$")
+	// make child start with a relative program path
+	cmd.Dir = dir
+	cmd.Path = fn
+	if runtime.GOOS == "openbsd" || runtime.GOOS == "aix" {
+		// OpenBSD and AIX rely on argv[0]
+	} else {
+		// forge argv[0] for child, so that we can verify we could correctly
+		// get real path of the executable without influenced by argv[0].
+		cmd.Args[0] = "-"
+	}
+	cmd.Env = append(cmd.Environ(), fmt.Sprintf("%s=1", executable_EnvVar))
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("exec(self) failed: %v", err)
+	}
+	outs := string(out)
+	if !filepath.IsAbs(outs) {
+		t.Fatalf("Child returned %q, want an absolute path", out)
+	}
+	if !sameFile(outs, ep) {
+		t.Fatalf("Child returned %q, not the same file as %q", out, ep)
+	}
+}
+
+func sameFile(fn1, fn2 string) bool {
+	fi1, err := os.Stat(fn1)
+	if err != nil {
+		return false
+	}
+	fi2, err := os.Stat(fn2)
+	if err != nil {
+		return false
+	}
+	return os.SameFile(fi1, fi2)
+}
+
+func init() {
+	if e := os.Getenv(executable_EnvVar); e != "" {
+		// first chdir to another path
+		dir := "/"
+		if runtime.GOOS == "windows" {
+			cwd, err := os.Getwd()
+			if err != nil {
+				panic(err)
+			}
+			dir = filepath.VolumeName(cwd)
+		}
+		os.Chdir(dir)
+		if ep, err := os.Executable(); err != nil {
+			fmt.Fprint(os.Stderr, "ERROR: ", err)
+		} else {
+			fmt.Fprint(os.Stderr, ep)
+		}
+		os.Exit(0)
+	}
+}
+
+func TestExecutableDeleted(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	switch runtime.GOOS {
+	case "windows", "plan9":
+		t.Skipf("%v does not support deleting running binary", runtime.GOOS)
+	case "openbsd", "freebsd", "aix":
+		t.Skipf("%v does not support reading deleted binary name", runtime.GOOS)
+	}
+	t.Parallel()
+
+	dir := t.TempDir()
+
+	src := filepath.Join(dir, "testdel.go")
+	exe := filepath.Join(dir, "testdel.exe")
+
+	err := os.WriteFile(src, []byte(testExecutableDeletion), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	out, err := testenv.Command(t, testenv.GoToolPath(t), "build", "-o", exe, src).CombinedOutput()
+	t.Logf("build output:\n%s", out)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	out, err = testenv.Command(t, exe).CombinedOutput()
+	t.Logf("exec output:\n%s", out)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+const testExecutableDeletion = `package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	before, err := os.Executable()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to read executable name before deletion: %v\n", err)
+		os.Exit(1)
+	}
+
+	err = os.Remove(before)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to remove executable: %v\n", err)
+		os.Exit(1)
+	}
+
+	after, err := os.Executable()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "failed to read executable name after deletion: %v\n", err)
+		os.Exit(1)
+	}
+
+	if before != after {
+		fmt.Fprintf(os.Stderr, "before and after do not match: %v != %v\n", before, after)
+		os.Exit(1)
+	}
+}
+`
diff --git a/src/os/executable_wasm.go b/src/os/executable_wasm.go
new file mode 100644
index 0000000..a88360c
--- /dev/null
+++ b/src/os/executable_wasm.go
@@ -0,0 +1,16 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build wasm
+
+package os
+
+import (
+	"errors"
+	"runtime"
+)
+
+func executable() (string, error) {
+	return "", errors.New("Executable not implemented for " + runtime.GOOS)
+}
diff --git a/src/os/executable_windows.go b/src/os/executable_windows.go
new file mode 100644
index 0000000..fc5cf86
--- /dev/null
+++ b/src/os/executable_windows.go
@@ -0,0 +1,32 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os
+
+import (
+	"internal/syscall/windows"
+	"syscall"
+)
+
+func getModuleFileName(handle syscall.Handle) (string, error) {
+	n := uint32(1024)
+	var buf []uint16
+	for {
+		buf = make([]uint16, n)
+		r, err := windows.GetModuleFileName(handle, &buf[0], n)
+		if err != nil {
+			return "", err
+		}
+		if r < n {
+			break
+		}
+		// r == n means n not big enough
+		n += 1024
+	}
+	return syscall.UTF16ToString(buf), nil
+}
+
+func executable() (string, error) {
+	return getModuleFileName(0)
+}